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Std 8 Science Chapter 9 Disaster Management Question Answer Maharashtra Board

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 9 Disaster Management Notes, Textbook Exercise Important Questions and Answers.

Class 8 Science Chapter 9 Disaster Management Question Answer Maharashtra Board

Class 8 Science Chapter 9 Disaster Management Textbook Questions and Answers

1. Answer the following in your own words.

Question a.
Explain the relation between continuous rains and landslide. Give reasons.
Answer:
Before the actual landslide, many changes occur in the surrounding hilly ground. The hard rocks develop cracks and crevices. These are natural changes but due to man-made activities, the cracks are widened due to erosion. These cracks make the big rocks to break into smaller stones. The cracks widen further due to excessive rainfall. These rocks further get eroded and they fall down along with soil from the slopes. The entire process is speeded up due to rainwater.

Question b.
Prepare a chart showing ‘Dos’ and ‘don’ts’ at the time of earthquake.
Answer:
At the time of earthquake

Question c.
What are the specifications of an earthquake-proof building?
Answer:
The earthquake-proof building is such that even if the earthquake is caused, it should not cause damage to the buildings due to these earth movements. There are some codes of conduct while constructing such buildings. Advanced technology is used for earthquake resistant construction. The foundation of earthquake-proof building is separated from lower land. The walls are of less weight or they are wooden. The house constructed with special light materials are preferred in earthquake-prone regions.

Question d.
Explain the effects of landslide.
Answer:
1. Mostly rivers originate in the hills and mountains. When there is landslide, the rivers naturally get flooded.
2. The paths of the riverine water changes due to landslide.
3. Waterfalls are displaced from their original positions.
4. New and artificial water reservoirs are created.
5. The falling debris, soil and rocks make the trees at the base of hillside uprooted. All the plant life is lost.
6. The constructions done by the villagers on the slope can be totally damaged due to landslide. There is large scale damage to property and life. In few cases like Malin the entire village was buried due to landslide and accompanied rainfall.
7. Transportation is affected as the roads and railway tracks are blocked due to debris.

Question e.
Is there any relation between dam and earthquake? Explain.
Answer:
There is abundant water stored in the dams. This water column puts additional weight on the ground. Initially there may not be any weight, but later due to construction of dam, suddenly the pressure of this weight is so high that this ground experiences the tension. If such area is already earthquake-prone, then there can be chances of earthquake. According to theory of plate tectonics, there are continuous movements in the earth’s surface. If over such fragile plates, the dams are constructed then the chances of earthquake are enhanced.

2. Give Scientific reasons.

Question a.
It is safer to find shelter under things like a bed, table at the time of earthquake.
Answer:
When earthquake takes place, due to the vibrations in the earth’s surface, there is possibility of the roof and walls of the house to fall. This collapse can cause severe head injury which can be fatal. Thus, one must take shelter below the hard-supporting structures such as bed or table. This precaution can save one’s life.

Question b.
In monsoon, don’t take shelter near hillside.
Answer:
The excessive rainfall can cause landslides. The soil and rocks from the hillside can be pushed down along with the flow of rainwater. This debris slides to the lower heights from the hills. This explains us that taking shelter near the base of the hillside can be disastrous as one can be buried in the debris due to sudden landslide. Therefore, in monsoon, one should not take shelter near hillside.

Question c.
Don’t use lifts at the time of earthquake.
Answer:
Lifts or elevators run on electricity. The electricity supply can be hindered due to earthquake. There may be chances of fire due to short circuit. We may get trapped in the elevator at such times. The building may also collapse due to earthquake. It is always better to use stairs at the time of such calamities, so that one can safely come out of the building. Therefore, it is said that lifts should not be used at the time of earthquakes.

Question d.
The foundation of earthquake- proof building is separated from lower land.
Answer:
The surface of the earth trembles at the time of earthquake. These tremors cause seismic waves which are responsible for the movements of the earth’s surface. The ground thus shakes or it goes up-down. These shocks and waves formed in the interior of the earth spread on the surface in all directions. This causes collapse of the building and other structures on the land.
To prevent such disasters the foundation of earth-quake proof building is separated from lower land.

3. If a crowd gathers at the place of earthquake, what would be the difficulties in relief work?

Question a.
If a crowd gathers at the place of earthquake, what would be the difficulties in relief work?
Answer:
If people flock in crowd, the rescue work will not be possible. The ambulances and the fire engines will not reach the spot where the help is needed. The personnel from disaster management cells cannot thus act in time. It will be difficult to manage the situation and thus such crowding should never be done.

4. Make a list of the institutes and organizations who provide help for disaster managment. Collect more information about their work.

Question a.
Make a list of the institutes and organizations who provide help for disaster management. Collect more information about their work.
Answer:
International government organisations working for disaster management are:
a. The United Nations and its organisations:
1. The Food and Agricultural Organisation of the UN (FAO): It gives early warning of impending food crises, and keep track of global food supply problems.
2. The United Nations Development Programme (UNDP): It helps disaster-prone countries with disaster mitigation, prevention and preparedness measures.
3. The World Food Programme (WFP): It is the main supplier of relief food aid.
4. The World Health Organisation (WHO): It gives global public health leadership by setting standards, monitoring health trends, and providing direction on emergency health issues. WHO’s role is to reduce avoidable loss of life and the burden of disease and disability.

b. The International Committee of the Red Cross ( ICRC): It gives physical rehabilitation to people injured by explosive weapons or other types of incident.

c. The International Federation of Red Cross and Red Crescent Societies ( IFRC): It coordinates and gives international help to victims of natural and technological disasters, to refugees and in health emergencies.

International non-governmental agencies working for disaster management are:
a. International Rescue Committee (IRC): It provides lifesaving care and life-changing help to refugees forced to flee from war or disaster.

b. IMA World Health: It, in collaboration with USAID, the World Bank and many other organisations, builds sustainable health care systems.

c. CARE: It is an organisation fighting global poverty. It works for women and puts efforts to improve their basic education, prevent the spread of HIV by providing awareness among them, give them increase access to clean water and sanitation, expand economic opportunity for them. It provides emergency aid to survivors of war and natural disasters, and helps people rebuild their lives.

Indian organisations and institutes working for disaster management are:
a. National Disaster Response Force (NDRF): The multi-disciplinary, multi-skilled, high-tech force of the NDMA are capable of dealing with all types of natural and man-made disasters.

b. National Disaster Management Authority (NDMA): It lay down the policies, plans and guidelines for Disaster Management to ensure timely and effective response to disasters.

c. National Institute of Disaster Management (NIDM): It has been given the responsibilities for human resource development, capacity building, training, research, documentation and policy advocacy in the field of disaster management.

5. Make a survey of your school according to the plan of disaster management an write the pointwise information.

Question a.
Make a survey of your school according to the plan of disaster managment an write the pointwise information.
Answer:

This an activity based questions. Kindly do it yourself. But make sure to involve the following points in your survey:

• Primary information of the school: It should include information such as name and address of the school and Head Master, total number of school staff and name and phone numbers of school management members.
• School disaster management committee: Get the information of the members involved in disaster management committee.
• Detailed information about school building: Note the number of rooms, classroom, age of the building, types of roofs under this point.
• Information about school ground: It should include information like distance of ground from the main road, types of play grounds.
• Daily routine of the school: It should include information like working time of the school, lunch break time for the school.
• Possible hazards in the school: It should information such as record of past disaster happened in school, current planning for overcoming disasters.
• Disaster management map of the school: It should have information regarding all the buildings of the school, entrances and exit gates, place of probable danger, safer place at the time of disaster.

6. Are there any possible places of landslide in your area? Collect information from experts.

Question a.
Are there any possible places of landslide in your area? Collect information from experts.
Answer:
This is an activity based question. kindly do it yourself.

7. With the help of the following pictures, explain your role in disaster management.

Question a.
With the help of following pictures, explain your role in the disaster management.
Answer:

The picture given is not very clear. It does not indicate the condition of disaster. Therefore, there are two alternatives for this answer.
Option 1 : The boy holds a paper on which is written, ‘I am at risk’! The boy is shocked to read this. Someone has given message to him. He must search that person and help him or her. He should therefore take help from some elder or from police force in such matter.

Option 2 : The boy shown in the picture is in danger. So, he is typing in his I – pad, “I am at Risk”. After receiving this message, someone will help him. It depends upon, to whom is he sending this message. If he sends this message to us, we can immediately try to help him. His message “I am at Risk”, shows that he is in danger and has to be saved.
It is not clear about which disaster is shown in the picture.

Project:

Question 1.
Make a collection of news, photos. and cuttings about landslides and rift collapse.

Question 2.
With the help of Internet, collect information about the latest gadgets and technology to forecast earthquake.

Question 3.
Collect information about NDRF, RPF, CRPF, NCC from Internet.

Question 4.
Discuss- Need of CCTV.

Class 8 Science Chapter 9 Disaster Management Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
Earthquakes cause ……………. waves leading to movements of the earth’s surface.
Answer:
Earthquakes cause seismic waves leading to movements of the earth’s surface.

Question 2.
The central point of earthquake is the point above the ……………. on the earth’s surface.
Answer:
The central point of earthquake is the point above the epicentre on the earth’s surface.

Question 3.
The accentuation of earthquake is measured in …………… .
Answer:
The accentuation of earthquake is measured in ‘Richter Scale’.

Question 4.
If there is earthquake at the bottom of ocean, it may create ……………… waves.
Answer:
If there is earthquake at the bottom of ocean, it may create tsunami waves.

Question 5.
…………….. is the best device to put off small fires.
Answer:
Stirrup pump is the best device to put off small fires.

Question 6.
………………. of waterfalls occurs due to landslides.
Answer:
Displacement of waterfalls occurs due to landslides.

State whether the following statements are True or False:

Question 1.
Every year nearly 2,400 to 4,000 earthquakes occur on the earth.
Answer:
False. (Every year nearly 12,400 to 14,000 earthquakes occur on the earth.)

Question 2.
Potassium, sodium and calcium are the metals that react with water at high room temperature.
Answer:
False. (Potassium, sodium and calcium are the metals that react with water at normal room temperature.)

Question 3.
A fire caused due to electrical components is extinguished by fire extinguishers like carbon dioxide are used.
Answer:
True.

Question 4.
Indiscriminate cutting of the trees results in improvement of soil quality.
Answer:
False. (Indiscriminate cutting of the trees results in soil erosion.)

Question 5.
Landslide results in loss of plant life.
Answer:
True.

Match the column:

Question 1.

Answer:

Question 2.

Answer:

Name the following:

Question 1.
Modern equipment to get prior intimation about earthquake:
Answer:

1. Laser ranging
2. Very long baseline
3. Geiger counter
4. Creep meter
5. Strain meter
6. Tide gauge
7. Tilt meter
8. Volumetric strain gauge.

Question 2.
Some code of conduct made by Indian Standard Institute for construction of buildings:
Answer:

1. IS 456
2. IS 1893
3. IS 13920

Question 3.
The subcommittees of School Disaster Management.
Answer:

1. Fire extinguisher
2. Awareness
3. Instructions
4. Traffic management
5. Safety
6. Communication committee.

Answer the following questions in one sentence:

Question 1.
Which is the instrument or machine that records the intensity of earthquake?
Answer:
The machine/Instrument which records the earthquakes is called ‘Seismograph’ or ‘Seismometer’.

Question 2.
Which is the most common and effective solution for extinguishing fire ?
Answer:
Spraying water is the most common and effective solution for extinguishing fire.:

Question 3.
Which type of fires can be extinguished by the method of suppressing?
Answer:
To extinguish the fires caused due to electricity or oil, the method of suppressing the fire can be used.

Question 4.
Which metals react with water at normal room temperature?
Answer:
Combustible metals like potassium, sodium and calcium, react with water at normal room temperature.

Question 5.
Which metals react with water at higher temperatures?
Answer:
Magnesium, aluminum and zinc react with water at high temperatures.

Question 6.
Which institutes have launched a program to forecast the landslides and its effects?
Answer:
The Government of India in collaboration with Indian Mountaineering Institute and International Centre for Integrated Mountain Development has launched a program to forecast the landslides and its effects.

Give scientific reasons:

Question 1.
The electric mains are shut off immediately after the earthquake.
Answer:
There is increased possibility of short circuit after the earthquake. This may result in fire. The earthquake has already – brought the disaster. To prevent further destruction, the electric mains are shut off immediately after the earthquake.

Write short notes:

Question 1.
Types of fire:
Answer:
There are five types of fire. This division is based on two criteria, viz.
(i) Which substance is being burnt, (ii) What is the method of extinguishing it.
1. Class A Fire: Commonly inflammable solid things such as wood, clothes, coal, papers can be burnt by this type of fire. This fire is extinguished by spraying water over it. This is also called cooling out. Water is effectively used to put off class A fire.

2. Class B Fire: Flammable liquid substances such as petrol, oil, varnish, solvents, cooking oil, paints, etc. catch fire and it is called class B fire. Since these substances are lighter than water, they can be extinguished only by foaming fire extinguishers.

3. Class C Fire: The fire caused due to gaseous substances is called class C fire. Domestic gas (L.P.G.) and acetylene can cause such kind of fire.

4. Class D Fire: Combustible metals catch class D fire. Metals such as potassium, sodium and calcium, can react with water at normal room temperature whereas magnesium, aluminium and zinc react with water at high temperature. When both these groups combine with water, it causes explosion.

5. Class E Fire: When electric components are subjected to fire, they form class C fire. Such fires can be caused by short circuit or due to problems in electric fittings. Such fire is extinguished with the help of carbon dioxide and non-conductive fire extinguishers.

Question 2.
Disaster relief – planning.
Answer:
Anyone can face disaster at any time. The only way to tackle with such disasters is to keep preparedness to deal with any calamity. Schools, colleges and various offices need to chalk out a detailed planning in case of possible disasters. With this purpose in mind, disaster relief planning is done.

E.g. In the disaster relief planning for school, primary information of the school, the structure of School Disaster Management Committee, detailed information about school building and information about school ground, daily routine of the school such as at what time the school starts and what time does it end, the possible hazards in the school, and disaster management map of the school is included.

Answer the following questions:

Question 1.
What are the different ways to extinguish fire? Write briefly about them.
Answer:
There are three main methods to extinguish the fire. These methods are used to stop the spread of fire and to avoid the financial and other losses.
1. Cooling out by use of water: Water is easily available and can be used for putting off fire instantly. Due to spraying of water, there is cooling effect produced which helps in reducing the loss by fire. Fire can be easily controlled by water.

2. Suppressing the fire by covering it: When there is a fire due to electricity or oil it has to be controlled by covering the fire by sand or soil. When the froth is spread on the fire, there is no contact between air and fire. This puts off the fire and stops the spread of fire caused due to oil.

3. Keep away Flammable Substances: Care is taken to keep away all flammable substances from the fire. Wooden articles and inflammable substances are kept in such as way the fire will not engulf it. Stirrup pumps are used to put off small fires by which the water is spread in all directions around the fire.

Question 2
What are the safety measures and precautions to stop the fire?
Answer:

1. Switching off the regulator of cooking gas cylinder when not in use. Put off the connections of all electrical appliances when not in use.
2. If there is fire, call others immediately for help. Take help of others by calling them. Also help others who are in need to save their lives from fire.
3. Get help from fire brigade by calling phone number 101.
4. Know details about working of the fire extinguishing apparatus.
5. Give first aid to the victim of fire. Seek immediate medical help,

Question 3.
What are the causes of landslide?
Answer:

1. Various types of natural disasters like earthquakes, tsunami, heavy rains, storms, floods can result into landslide.
2. The indiscriminate cutting down of the trees can result into soil erosion. Soil erosion in turn results into landslide.
3. The construction of roads, bridges, railway tracks, etc. on the mountain slopes result into lot of digging. Such activities make soil cover loose. From the slopes the soil and rocks then can slide easily. This results into landslides.

Draw a well labelled diagrams:

Question 1
Seismometer/Secismograph.
Answer:

Question 2.
Focal point and epicenter or earthquake.
Answer:

Open-Ended Questions:

Question 1.
Have you at any time faced with any disaster? What were your experiences during such condition? How did you get rescued?
Answer:
Students should write their own experiences about such incidents if any.

Question 2.
In Maharashtra where do the traffic jams occur due to landslides? Make a list of such places. Why does the landslide occur at those places only? Discuss in the classroom and suggest preventive measures.
Answer:
In Maharashtra, the landslides are very common in the hilly regions. The traffic is suspended often during rainy season when such calamity strikes. Malshej, Khandala, Kasara are some of the Ghats which are very prone to land-slide. On the tracks of Konkan railway, the landslides are very common during heavy downpour.

The regions where more landslides occur have many constructions and large scale deforestation. The traffic of Konkan railway comes to standstill after such landslide. Moreover, during heavy monsoon days, the speed of the running trains is kept very slow. The soil structure is also responsible for such landslides.

Preventive measures: There should be wire meshing done across the sides of the roads and railway tracks so that the collapsed rocks and other debris does not obstruct the traffic. Tree plantation should be carried out to prevent loosening of the soil and rock. It will also help in preventing the soil erosion.

Balbharati Maharashtra State Board 8th Std Science Textbook Solutions 

• Living World and Classification of Microbes Class 8 Science Textbook Solutions
• Health and Diseases Class 8 Science Textbook Solutions
• Force and Pressure Class 8 Science Textbook Solutions
• Current Electricity and Magnetism Class 8 Science Textbook Solutions
• Inside the Atom Class 8 Science Textbook Solutions
• Composition of Matter Class 8 Science Textbook Solutions
• Metals and Nonmetals Class 8 Science Textbook Solutions
• Pollution Class 8 Science Textbook Solutions
• Disaster Management Class 8 Science Textbook Solutions
• Cell and Cell Organelles Class 8 Science Textbook Solutions

Std 6 Science Chapter 15 Fun with Magnets Question Answer Maharashtra Board

Balbharti Maharashtra State Board Class 6 Science Solutions Chapter 15 Fun with Magnets Notes, Textbook Exercise Important Questions and Answers.

Class 6 Science Chapter 15 Fun with Magnets Question Answer Maharashtra Board

1. How will you do this?

Question a.
Determine whether a material is magnetic or non-magnetic.
Answer:

1. To determine whether the material is magnetic or non-magnetic, a magnet is moved over it.
2. If the material sticks to the magnet, it is called magnetic material.
3. If the material does not stick to the magnet, it is non-magnetic.

Question b.
Explain that a magnet has a certain magnetic field.
Answer:

1. The space around a magnet in which the magnetic force is active is called the magnetic field.
2. Place a white paper on a drawing board and place a bar magnet in the middle of the paper.
3. Spread the iron filings on the sheet and gently tap the sheet.
4. The iron filings arrange around the magnet in definite curved lines forming a symmetric pattern.
5. The lines are closer to each other near the poles and less crowded in the middle region around the magnet.
6. Beyond a particular region, the iron filings, will not get attracted.
7. The region where iron filings are attracted is the magnetic field of the magnets.

Question c.
Find the north pole of a magnet.
Answer:

1. Take a bar magnet. Tie a thread to the centre of a bar magnet and hang it from a stand.
2. Note the direction in which the magnet settles and turn it around again.
3. Allow it to settle and note the direction.
4. The end of the magnet that points to the north is called the north pole, while the end that points to the south is called the south pole.
5. The north pole is indicated by ‘N’ and the south pole by ‘S’.

2. Which magnet will you use?

Question a.
Iron is to be separated from a trash.
Answer:

1. Sharp and heavy iron scrap material is attached to a big disc.
2. The disc is a magnet and all scrap is attracted to it.
3. It is not possible to create, store such a big size magnet. Therefore magnetism is induced in the disc with the help of electricity.

An electromagnet is used which is attached to a crane for loading and unloading, transporting scrap and loose iron material from a trash.

Question b.
You are lost in a forest.
Answer:

1. If we are lost in a forest, we should take help of a mariner’s compass which will help us to find the directions while travelling through unknown regions.
2. If mariner’s compass is not available, a bar magnet when suspended in the centre will rest in north-south direction.

Question c.
A window shutter opens and shuts continuously in the wind.
Answer:
A bar magnet can be attached to the window pane so that the window will be closed tight during strong winds also.

3. Fill in the blanks with appropriate word.

Question a.
If a bar magnet is hung by a thread tied at its centre, its north pole becomes steady in the direction of the …………… pole of the earth. (south, north, east, west)
Answer:
North

Question b.
If a bar magnet is cut into equal pieces by cutting it at right angles to its axis at two pieces …………… bar magnets are formed, and a total of …………… poles are formed. (6,3,2)
Answer:
3, 6

Question c.
There is a repulsion between the …………… poles of a magnet and attraction between its ……………. poles. (opposite, like.)
Answer:
like, opposite

Question d.
When magnetic material is taken close to a magnet, the material acquires …………… . (permanent magnetism, induced magnetism, temporary, magnet keeper)
Answer:
induced magnetism

Question e.
If a magnet attracts a piece of metal, that piece must be made of ………… .(any other metal but iron, magnetic material or iron, non-magnetic material, electromagnets)
Answer:
magnetic material or iron

Question f.
A magnet remains steady in a ………….. direction. (east-west, north-south,)
Answer:
north-south

4. Write the answers in your words.

Question a.
How is an electromagnet made?
Answer:
1. To make an electromagnet we need the following apparatus; An iron nail of 10 cm length, 1 metre long insulated copper wire, a battery cell, pins.
2. Wind the copper wire around the nail as shown in the figure. Connect the free ends of the wire to the two terminals of a cell through a plug key.
3. Close the key to complete the circuit.
4. Bring small pins near the tip of the nail and observe.
5. When the circuit is completed, the iron pins are attracted by the nail and hence, they stick to the nail.

6. When the circuit is broken, the pins fall off.
7. A magnet is prepared by passing an electric current through an insulated wire wound around the iron nail. This is an electromagnet.
8. When the current is allowed to pass, the nail becomes a magnet and attracts pin / pins stick to it.
9. When the current is put off the nail does not behave as a magnet and therefore, pins fall off.
10. The magnetism is temporary in the case of an electromagnet.

Question b.
Write the properties of a magnet.
Answer:
Magnet possess following properties/ characteristics.

1. Magnet always settles in the north-south direction.
2. The magnetic force is concentrated at the two ends or poles of a magnet.
3. If a magnet is divided into two parts, two independent magnets are formed. It means that the two poles of a magnet cannot be separated from each other.
4. A magnetic material acquires magnetism when placed near a magnet. This magnetism is called induced magnetism.
5. There is repulsion between like poles of a magnet, while there is attraction between the opposite poles.

Question c.
What are the practical uses of a magnet?
Answer:

1. Magnets are materials to which objects made from iron, nickel, cobalt are attracted. But man explored magnets and its properties and made his life comfortable.
2. Permanent Magnets: are used in caps of pin holders, doors of fridges, doors of cupboards etc.
3. Temporary magnets: Electromagnets are used in electric bells, circuit of various machines, ATM card swipe machines, MRI- Magnetic Resonance Image, loudspeakers, electric cranes, microphones, Mariner’s compasses, etc.

Activity

Question 1.
Collect information regarding how the various magnets used in our day-to-day tasks are produced.

Question 2.
Collect information about the magnetism of the earth.

Class 6 Science Chapter 15 Fun with Magnets Important Questions and Answers

Fill in the blanks.

Question 1.
Iron objects ………….. to a magnet.
Answer:
stick

Question 2.
A magnet is used in ………….. and ………….. .
Answer:
gadgets and machines

Question 3.
The materials that stick to a magnet are called ………….. materials.
Answer:
magnetic

Question 4.
Materials that do not stick to a magnet are called ………….. materials.
Answer:
non-magnetic

Question 5.
When a magnet attracts an object, that object is ………….. due to the magnetic force.
Answer:
displaced

Question 6.
Magnetism is a form of ………….. .
Answer:
energy

Question 7.
A magnet always settles in the ………….. direction.
Answer:
north-south

Question 8.
The north pole is indicated by’ …………… and the south pole by ‘……………’.
Answer:
‘N’-‘S’

Question 9.
The end of the magnet that points to the north is called the ………….. .
Answer:
Northpole

Question 10.
The end of the magnet that points to the south is called the ………….. .
Answer:
South pole

Question 11.
The magnetic force is concentrated at the two ends or ………….. of a magnet.
Answer:
poles

Question 12.
If a magnet is divided into two parts, two ………….. magnets are formed.
Answer:
independent

Question 13.
It means that the two poles of a magnet cannot be ………….. from each other.
Answer:
separated

Question 14.
A magnetic material acquires magnetism when placed near a
Answer:
magnet

Question 15.
Iron filling stick to the iron bar when the ………….. is near it.
Answer:
magnet

Question 16.
There is ………….. between like poles of a magnet.
Answer:
repulsion

Question 17.
There is ………….. between the opposite poles of a magnet.
Answer:
attraction

Question 18.
Magnetic objects ………….. magnetism.
Answer:
induce

Question 19.
Material ………….. is a mixture of aluminium, nickel and cobalt.
Answer:
Alnico

Question 20.
………….. magnets are made from a mixture of nickel, cobalt and iron.
Answer:
Permanent

Question 21.
The bar of soft or pure iron which protects a magnet is called ………….. .
Answer:
magnet keeper

Question 22.
Magnetism gets ………….. when a magnet is heated, thrown, knocked about or broken into pieces.
Answer:
destroyed

Question 23.
Electromagnetic energy is used in our ………….. life.
Answer:
day-to-day

Question 24.
The metals iron, cobalt, nickel are ………….. materials.
Answer:
magnetic

Question 25.
………….. is a natural magnet.
Answer:
Magnetite

Match the columns.

Question a.

Answer:

State whether true or false. If false, correct the statement.

Question 1.
Material alnico is a mixture of aluminium, nickel and iron.
Answer:
False: Material alnico is a mixture ofaluminium, nickel and cobal.

Question 2.
Magnetism of electromagnet is permanent.
Answer:
False: Magnetism of electromagnet is temporary.

Question 3.
The bar of soft or pure iron protects the magnet.
Answer:
True

Question 4.
Like poles attract each other and unlike poles repel each other.
Answer:
False: Like poles repel each other and unlike poles attract each other.

Question 5.
The magnetic force is concentrated at the centre of the magnet.
Answer:
False: The magnetic force is concentrated at the poles of the magnet

Question 6.
Magnetism is a kind of energy.
Answer:
True

Question 7.
Mariner’s compass is used for finding directions while travelling.
Answer:
True

Question 8.
Cobalt is a magnetic material.
Answer:
True

Question 9.
The north pole is indicated by ‘S’ and the south pole is indicated by ‘N’.
Answer:
False: The north pole is indicated by Wand the south pole is indicated by ‘S’.

Question 10.
Electromagnetism is used in many places in our day-to-day life.
Answer:
True

Answer the following questions in one sentence.

Question 1.
What is a magnet?
Answer:
The material to which objects made from iron, nickel, cobalt get attracted is called as magnet.

Question 2.
What is magnetism?
Answer:
The property of a material to which objects made from iron, nickel, cobalt get attracted is called as magnetism.

Question 3.
What are magnetic materials?
Answer:
Materials that stick to a magnet are called magnetic materials, e.g. cobalt, nickel, iron.

Question 4.
What are non-magnetic materials?
Answer:
Materials that do not stick to a magnet are called non-magnetic material, e.g. plastic, rubber, glass etc.

Question 5.
What are lodestones?
Answer:
Lodestones are leading stones which are used for finding the directions while travelling through unknown regions.

Question 6.
How is magnetism a kind of energy?
Answer:
Work is done by magnetic force. Thus, magnetism is a kind of energy.

Question 7.
What is an electromagnet?
Answer:
When magnetism is produced in the iron due to the electric current, it is called an electromagnet.

Question 8.
How are permanent magnets made?
Answer:
Permanent magnets are made from a mixture of nickel, cobalt and iron.

Question 9.
List the instruments where electromagnets are used.
Answer:
Electromagnets are used in doorbells, cranes, loudspeakers, voltameters, TVs, antennas, radios etc.

Question 10.
How is magnetism destroyed?
Answer:
When magnets are heated, thrown, knocked about or broken into pieces, magnetism gets destroyed.

Question 11.
What is a magnet keeper?
Answer:
A magnet keeper is a bar of soft or pure iron which protects a magnet. It is a piece of soft iron placed in the box in which a magnet is kept.

Question 12.
Magnets exist in variety of shapes.
Answer:
Today, magnets are used in many machines, gadgets and devices. They are all man-made. Hence, they can have a variety of shapes depending upon their use.

Answer the following briefly.

Question 1.
What are leading stones?
Answer:

1. It was known quite long ago to the people in China and Europe that a piece of magnetite, hung freely always settled in the north-south direction.
2. These rocks then came to be used for finding the directions while travelling through unknown regions.
3. That is why they are called leading stones or Lodestones.

Question 2.
What has led to the invention of the Mariner’s compass?
Answer:
Leading stones have led to the invention of the mariner’s compass.

Question 3.
List the different shapes of magnets.
Answer:

1. Magnets have a variety of shapes depending on their uses.
2. They are bar magnets, disc magnets, horseshoe magnets, ring shaped magnets, cylindrical magnets, and small button magnets.

Question 4.
What are permanent magnets?
Answer:

1. Magnets which do not lose their magnetism easily are called permanent magnets or Magnets which are made up of magnetic substances are permanent magnets.
2. e.g. Magnets fixed in a pin holder, magnets of a door of a cupboard are permanent magnets.
3. Permanent magnets are made from a mixture of
   • Nickel, cobalt, iron
   • Aluminium, nickel, cobalt – alnico

Give scientific reasons.

Question 1.
Why is it important to place a magnet keeper in a box along with magnets?
Answer:
Magnetism gets destroyed when a magnet is heated, thrown, knocked about or broken into pieces. A magnet keeper which is a bar of soft or pure iron protects a magnet.

Question 2.
Cranes with magnets are used.
Answer:
When a magnet attracts an object, that object is displaced due to the magnetic force. In factories, ports, garbage depots, large objects are lifted and shifted from place to place using cames. Hence cranes are fitted with magnets.

Can you tell?

Question 1.
Pins in a pin holder do not fall? While we are shutting the door of a fridge, we find that it closes automatically from certain distance and does not open unless pulled again.
Answer:
Magnet is fitted in the cap of a pin holder and in the door of a fridge. Iron objects stick to the magnet.

Question 2.
Take a magnet from the laboratory and bring it near various objects in your use. Which of them stick to the magnet? What material is each of them made of? Observe these things carefully. Classify the objects into two groups: those which stick to the magnet, those which do not.
Comb, table, cupboard – iron, spoon, scissors, pen, pencil, eraser, books, mobile, laptops, glass bangles, hair pin, cupboard handle, chair, steel lunch box, magnetic stickers, toys, gold ring.
Answer:

Question 3.
Take a mixture of sand, pieces of paper, sawdust, iron filings and pins in a saucer and pass a magnet around the mixture. What do you see?
Answer:
When magnet is moved over a mixture of sand, pieces of paper, sawdust, iron filings and pins, pins and iron filings will cling to the magnet. Sand, sawdust and pieces of paper will remain behind.

Question 4.
How is a Mariner’s Compass used?
Answer:

1. A Mariner’s Compass is a magnetic needle used in navigation to show direction by deflections.
2. It is a direction-finding instrument used in navigation.
3. It is placed on the maps, grounds, decks as it will point to the magnetic north pole.
4. It has two or more magnets permanently attached to a compass card which moves freely on a pivot.
5. The needle fixed on the compass bowl indicates the ship’s heading position.

Question 5.
Find out where the magnet given are used?
Answer:

Question 6.
Identify the different types of magnets as shown in the picture below.
Answer:
a. Circular magnet
b. Cylindrical magnet
c. Horseshoe magnet
d. Bar magnet

Maharashtra State Board Class 6 Science Textbook Solutions

• Work and Energy Class 6 Science Textbook Solutions
• Simple Machines Class 6 Science Textbook Solutions
• Sound Class 6 Science Textbook Solutions
• Light and the Formation of Shadows Class 6 Science Textbook Solutions
• Fun with Magnets Class 6 Science Textbook Solutions
• The Universe Class 6 Science Textbook Solutions

Std 8 Science Chapter 5 Inside the Atom Question Answer Maharashtra Board

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 5 Inside the Atom Notes, Textbook Exercise Important Questions and Answers.

Class 8 Science Chapter 5 Inside the Atom Question Answer Maharashtra Board

Class 8 Science Chapter 5 Inside the Atom Textbook Questions and Answers

1. Answer the following.

Question a.
What is the difference in the atomic models of Thomson and Rutherford?
Answer:

Question b.
What is meant by valency of an element? What is the relationship between the number of valence electron and valency?
Answer:
Valency: The capacity of an ; element to combine with another element is known as valency.
Valence electrons: The electrons in the outermost shell of an atom of an element are called valence electrons.
Helium and neon, atoms of both these gaseous element do not combine with any other atom. These elements are chemically inert, i.e. their valency is zero.

Helium atom contains two electrons, indicates that the outermost shell of helium has an electron duplet. The valence shell of neon is completely filled, i.e. neon has an electron octet. Similarly argon contains eight electrons in the valence shell, i.e. argon has an electron octet. It is confirmed that the valency is zero when electron octet (or duplet) is complete.

Atoms of all the elements except inert gases have tendency to combine with other atoms, i.e. they have a non zero valency. The molecules formed by combination with hydrogen (E.g. H₂, HCl) that valency of hydrogen is one. The electronic configuration of hydrogen shows that there is one electron less than the complete duplet state. This number ‘one’ matches with the valency of hydrogen which is also one.

It means that there is relationship between the valency of an element and the number of electrons in its valence shell.

Question c.
What is meant by atomic mass i number? Explain how the atomic number and mass number of carbon are 6 and 12 respectively.
Answer:
The total number of protons and neutrons in the nucleus of the atom is called the atomic mass number. The atomic number, i.e. the proton number of carbon is 6 and the mass number is total number of protons and neutrons in the carbon, i.e. 6 protons + 6 neutrons = 12. Therefore, the atomic number and mass number of carbon are 6 and 12 respectively.

Question d.
What is meant by subatomic particle? Give brief information of three subatomic particles with reference to electrical charge, mass and location.
Answer:
A particle which is a constituent of an atom hence smaller than the atom is called subatomic particle.
An atom is formed from the nucleus and the extranuclear part. These contain three types of subatomic particles.
The nucleus contains two types of subatomic particles together called nucleons. Protons and neutrons are the two types of nucleons or subatomic particles and electrons are subatomic particles in the extra nuclear part.

1. Proton (p): Proton is a positively charged subatomic particle in the atomic nucleus. The positive charge on the nucleus is due to the proton in it. A proton is represented by the symbol ‘p’. Each proton carries a positive charge of +1e. (1e = 1.6 × 10^-19 coulomb). When total positive charge on the nucleus is expressed in the unit ‘e’, its magnitude is equal to the number of proton in the nucleus.
The mass of one proton is approximately lu (1 Dalton).
(1u = 1.66 × 10^-27g) (The mass of one hydrogen atom is also approximately lu.)

2. Neutron (n): Neutron is an electrically neutral subatomic particle and is denoted by the symbol ‘n’. The number of neutron in the nucleus is denoted by the symbol ‘N’ Atomic nuclei of all the elements except hydrogen with atomic mass lu, contain neutrons. The mass of a neutron is approximately lu, which is almost equal to that of a proton.

3. Electron (e^–): Electron is a negatively charged subatomic particle and is denoted by the symbol ‘e-’. Each electron carries one unit of negative charge (-1e). Mass of an electron is 1800 times less than that of a hydrogen atom. Therefore the mass of an electron can be treated as negligible. Electron in the extranuclear part revolve in the discrete orbits around the nucleus. The energy of an electron is determined by the shell in which it is present.

2. Give scientific reasons:

Question a.
All the mass of an atom is concentrated in the nucleus.
Answer:

1. The nucleus of an atom contains protons and neutrons.
2. The electrons revolve around the nucleus.
3. The mass of an electron is negligible compared to that of a proton or a neutron.
4. Hence, the mass of an atom depends mainly on the number of protons and neutrons. Therefore, practically all the mass of an atom is concentrated in the nucleus.

Question b.
Atom is electrically neutral.
Answer:

1. An atom is made of two parts, viz. the nucleus and the extranuclear part.
2. The nucleus is positively charged. The positive charge on the nucleus is due to protons.
3. The extranuclear part of an atom is made of negatively charged electrons.
4. In an atom, the number of protons is equal to the number of extranuclear electrons.
5. The magnitude of the positive charge on the nucleus equals the magnitude of the negative charge on the electrons. As the opposite charges are balanced, the atom is electrically neutral.

Question c.
Atomic mass number is a whole number.
Answer:

1. The total number of protons and neutrons in the nucleus of the atom is called the atomic mass number (A).
2. As protons and neutrons are whole numbers, the atomic mass number is also a whole number.

Question d.
Atoms are stable though negatively charged electron are revolving within it.
Answer:

1. The entire mass of the atom is concentrated in the nucleus and the positively charged nucleus at centre of an atom.
2. The negatively charged electrons revolve around the nucleus.
3. The total negative charge on all the electron is equal to positive charge on the nucleus. As the opposite charges are balanced, the atom is stable.

3. Define the following terms.

Question a.
Atom:
Answer:
An atom is the smallest particle of an element which retains its chemical identity in all physical and chemical changes.

Question b.
Isotope
Answer:
Atoms of the same element having the same atomic number, but different atomic mass numbers are called isotopes.

Question c.
Atomic number
Answer:
The number of electrons or protons in an atom is called the atomic number. It is denoted by Z.

Question d.
Atomic mass number
Answer:
The total number of protons and neutrons in the nucleus of the atom is called the atomic mass number. It is denoted by A.

Question e.
Moderator in nuclear reactor
Answer:
The substance which reduces the speed of fast-moving neutrons produced in a fission is called a moderator.

4. Draw a neal labelled diagram.

Question a.
Explain Rutherford’s scattering experiment.
Answer:

Alpha particles emitted by radioactive element bear a positive charge. Rutherford bombarded alpha particles through a very thin gold foil. He observed the path of α – particles by means of a fluorescent screen around the gold foil. It was expected that

1. Most of the alpha particles passed through the gold foil without any deviation.
2. Some alpha particles were deflected from their path through small angles.
3. A few alpha particles were scattered at large angles.
4. A still smaller number of same sign particles get deflected through a larger angle and one a-particle out of 20000 bounced back in the direction opposite to the original path.

Question b.
Thomson’s atomic model.
Answer:
Thomson’s plum pudding model of atom:

1. According to Thomson’s model the positive charge is distributed throughout the atom and the negatively charged electron: are embedded in a gel of positive charge (a plum pudding model).
2. The distributed positive charge is balanced by the negative charge on the electrons. Therefore the atom becomes electrically neutral.

Question c.
Diagrammatic sketch of electronic configuration of magnesium (Atomic number 12).
Answer:

Question d.
Diagrammatic sketch of electronic configuration of argon (Atomic number 18).
Answer:

5. Fill in the blanks.

Question 1.
Electron, proton, neutron are the types of ………… in an atom.
Answer:
Electron, proton, neutron are the types of subatomic particles in an atom.

Question 2.
An electron carries a ……………. charge.
Answer:
An electron carries a negative charge.

Question 3.
The electron shell ………….. is nearest to the nucleus.
Answer:
The electron shell K is nearest to the nucleus.

Question 4.
The electronic configuration of magnesium is 2, 8, 2. From this it is understood that the valence shell of Magnesium is …………….. .
Answer:
The electronic configuration of magnesium is 2, 8, 2. From this it is understood that the valence shell of Magnesium is M.

Question 5.
The valency of hydrogen is one as per the molecular formula H₂O. Therefore valency of ‘Fe’ turns out to be ………….. as per the formula Fe₂O₃.
Answer:
The valency of hydrogen is ‘one’ as per the molecular formula H₂O. Therefore valency of ‘Fe’ turns out to be 3 as per the formula Fe₂O₃.

6. Match the pairs.

Question 1.

Answer:

7. Deduce from the datum provided.

Question 1.

Answer:
1. There are 12 neutrons in the sodium \(\left({ }_{11}^{23} \mathrm{Na}\right)\).
(N = A – Z) 23 – 11 = 12
2. Atomic mass number of \({ }_{6}^{14} \mathrm{C}\) is 14.
3. There are 17 protons in chlorine \(\left({ }_{37}^{17} \mathrm{Cl}\right)\)

Project:

Explain the atomic models using the material such as old C.D., balloon, thread, marbles, etc.

Class 8 Science Chapter 5 Inside the Atom Additional Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
An atom is electrically ……………. .
Answer:
An atom is electrically neutral.

Question 2.
Except hydrogen, the nuclei of all atoms contain ………….. .
Answer:
Except hydrogen, the nuclei of all atoms contain neutrons.

Question 3.
\({ }_{6}^{12} \mathrm{C}\), …………… and …………. are isotopes of carbon.
Answer:
\({ }_{6}^{12} \mathrm{C}\), \({ }_{6}^{13} \mathrm{C}\) and \({ }_{6}^{14} \mathrm{C}\) are isotopes of carbon.

Question 4.
An atom has 11 protons and …………. neutrons and hence its atomic mass number is 23.
Answer:
An atom has 11 protons and 12 neutrons and hence its atomic mass number is 23.

Question 5.
The element ………….. has two electrons in the K shell, but it is a noble gas.
Answer:
The element helium has two electrons in the K shell, but it is a noble gas.

Question 6.
Isotopes of the element have the same ……….. properties.
Answer:
Isotopes of the element have the same chemical properties.

Question 7.
Electrons must absorb …………….. to transit between orbits.
Answer:
Electrons must absorb energy to transit between orbits.

Question 8.
……….. discovered the electron.
Answer:
J. J. Thomson discovered the electron.

Question 9.
∝ – particles have ………….. charge.
Answer:
∝ – particles have positive charge.

Question 10.
Electrons revolve around the …………….. in certain discrete orbits.
Answer:
Electrons revolve around the nucleus in certain discrete orbits.

Question 11.
The shell-wise distribution of electrons is called the ………………… .
Answer:
The shell-wise distribution of electrons is called the electronic configuration.

Question 12.
Democritus termed the smallest particles of matter as …………… .
Answer:
Democritus termed the smallest particles of matter as atoms.

Question 13.
………………. discovered neutron.
Answer:
James Chadwick discovered neutron.

Question 14.
Electrons revolve around the nucleus in paths called ………….. .
Answer:
Electrons revolve around the nucleus in paths called orbits.

Question 15.
The second shell has the capacity of ……………… .
Answer:
The second shell has the capacity of 8 electrons.

Question 16.
Electrons in the ………….. shell have minimum energy.
Answer:
Electrons in the K or first shell have minimum energy.

Question 17.
Electrons in an atom occupy shells in increasing order of …………… .
Answer:
Electrons in an atom occupy shells in increasing order of energy.

Question 18.
Atomic masses are measured in a unit called …………… .
Answer:
Atomic masses are measured in a unit called dalton.

Question 19.
According to the atomic model of …………….., electrons are embedded in a gel of positive charge.
Answer:
According to the atomic model of Thomson, electrons are embedded in a gel of positive charge.

Question 20.
All atoms, except ………….. contain neutrons in their nuclei.
Answer:
All atoms, except normal hydrogen contain neutrons in their nuclei.

Question 21.
The maximum capacity of the M shell is ………………… electrons.
Answer:
The maximum capacity of the M shell is 18 electrons.

Question 22.
The atom of the element ……………. has eight electrons in the outermost shell.
Answer:
The atom of the element neon has eight electrons in the outermost shell.

Rewrite the following statements selecting the correct options:

Question 1.
The symbol A is used to denote the …………. .
(a) atomic number
(b) atomic radius
(c) atomic mass number
(d) atomic mass
Answer:
(c) atomic mass number

Question 2.
The existence of isotopes is due to the presence of different number of …………….. .
(a) electrons
(b) protons
(c) neutrons
(d) positrons
Answer:
(c) neutrons

Question 3.
In the nucleus of a sodium atom (\({ }_{11}^{23} \mathrm{Na}\)), there are ……………… neutrons.
(a) 11
(b) 12
(c) 10
(d) 9
Answer:
(b) 12

Question 4.
Isotopes of an element have the same number of …………….. .
(a) neutrons
(b) nucleons
(c) electrons
(d) atoms
Answer:
(c) electrons

Question 5.
The great Indian philosopher ………….. proposed that matter is made up of invisible tiny particles.
(a) Aryabhatta
(b) Kanad
(c) Bhaskaracharya
(d) Chanakya
Answer:
(b) Kanad

Question 6.
The maximum capacity of the M shell is …………… electrons.
(a) 2
(b) 8
(c) 18
(d) 32
Answer:
(c) 18

Question 7.
The mass of the electron is …………….. times less than that of a hydrogen atom.
(a) 1800
(b) 8100
(c) 1550
(d) 1600
Answer:
(a) 1800

Question 8.
The L shell is the valence shell in …………. .
(a) hydrogen
(b) chlorine
(c) oxygen
(d) sodium
Answer:
(c) oxygen

Question 9.
The M shell is the valence shell in ……………….. .
(a) fluorine
(b) neon
(c) carbon
(d) chlorine
Answer:
(d) chlorine

Question 10.
The N shell is the valence shell in ………….. .
(a) fluorine
(b) chlorine
(c) bromine
(d) helium
Answer:
(c) bromine

Question 11.
The maximum capacity of the N shell is ……………. electrons.
(a) 2
(b) 32
(c) 18
(d) 8
Answer:
(b) 32

Question 12.
The maximum number of electrons that can be accommodated in the third orbit is ………… .
(a) 3
(b) 8
(c) 32
(d) 18
Answer:
(d) 18

Question 13.
Rutherford alpha-particle scattering experiment was responsible for the discovery of the ………………. .
(a) atomic nucleus
(b) proton
(c) electron
(d) atomic mass
Answer:
(d) atomic mass

Question 14.
Isotopes of element have …………….. .
(a) different atomic numbers and different atomic mass
(b) different atomic numbers but the same atomic mass number
(c) the same atomic number but different atomic mass numbers
(d) the same atomic number and the same atomic mass number
Answer:
(c) the same atomic number but different atomic mass numbers

Question 15.
The nucleus of an atom contains 19 protons and 21 neutrons. The atomic mass number of the element is ………….. .
(a) 19
(b) 21
(c) 40
(d) 39
Answer:
(c) 40

Question 16.
The nucleus of an atom contains 18 protons and 22 neutrons. The atomic number of the element is ……………… .
(a) 18
(b) 40
(c) 22
(d) 4
Answer:
(a) 18

Question 17.
When writing the symbol of its …………… and ………….. are written.
(a) atomic number, atomic mass number
(b) protons, electrons
(c) protons, neutrons
(d) atomic number, electrons
Answer:
(a) atomic number, atomic mass number

Question 18.
The particles in the atomic nucleus are …………….. .
(a) protons and electrons
(b) electrons
(c) electrons and neutrons
(d) protons and neutrons
Answer:
(d) protons and neutrons

State whether the following statements are True or False:

Question 1.
An atom as a whole is electrically neutral
Answer:
True.

Question 2.
The mass of an atom is distributed evenly within it.
Answer:
False. (The mass of atom is not distributed evenly, practically all the mass is concentrated in the nucleus.)

Question 3.
The electron has the same mass as that of the proton.
Answer:
False. (The mass of the electron is much less than that of the proton.)

Question 4.
The electron in the K shell has maximum energy.
Answer:
False. (The electrons in the K shell has minimum energy.)

Question 5.
Isotopes have same atomic number but different atomic mass number.
Answer:
True.

Question 6.
Matter is composed of molecules and molecules are made of atoms.
Answer:
True.

Question 7.
In India, total 22 nuclear reactors in eight places are functioning.
Answer:
True.

Question 8.
The number of electrons in a given orbit is given by the formula n
Answer:
False. (The number of electrons in a given orbit is given by the formula 2n2)

Question 9.
Atomic masses are measured in a unit called the dalton (u).
Answer:
True.

Question 10.
The chemical properties of isotopes are different.
Answer:
False. (The chemical properties of isotopes are the same.)

Question 11.
The maximum capacity of the N shell is 18 electrons.
Answer:
False. (The maximum capacity of the N shell is 32 electrons.)

Question 12.
Deuterium is an isotope of hydrogen.
Answer:
True.

Question 13.
Isotopes are used in the treatment of cancer.
Answer:
True.

Question 14.
Atoms of all elements, except normal hydrogen contain neutrons.
Answer:
True.

Question 15.
Electrons moving in different orbits possess the same amount of energy.
Answer:
False. (Electrons moving in different orbits possess different amounts of energy.

Question 16.
Rutherford discovered the neutron.
Answer:
False. (Chadwick discovered the neutron.)

Question 17.
The nth orbit contains at the most 2n² electrons.
Answer:
True.

Question 18.
Electrons have different energies according to their orbits.
Answer:
True.

Question 19.
The capacity of the second orbit is 18 electrons.
Answer:
False. (The capacity of the second orbit is 8 electrons.)

Question 20.
The radioactive isotope Sodium-24 is used in the medical treatment of cancer.
Answer:
False. (The radioactive isotope Sodium-24 is used for detection of cracks in the underground pipes.)

Question 21.
Uranium-235 is used in the production of electricity.
Answer:
True.

Consider the relation between I the items in the first pair and write the correlation for second pair:

Question 1.
K : 2 : M : …………. .
Answer:
18

Question 2.
Carbon : 2, 4 : : Fluorine : …………….. .
Answer:
2, 7

Question 3.
Nitrogen : Valency three : : Fluorine : …………….. .
Answer:
valency one

Question 4.
Atomic radius : pm : Atomic mass : ……………. .
Answer:
u

Question 5.
NaH : Valency of Na : 1 : : MgCl₂ : Valency of Mg …………… .
Answer:
2

Question 6.
\(35 \mathrm{Cl}\) : number of neutrons 18 : : \({ }^{37} \mathrm{Cl}/latex] : …………….. .
Answer:
number of neutrons 20

Question 7.
Protons : Positive : : ……………. : Neutral.
Answer:
Neutrons.

Match the following:

Question 1.

Answer:

Question 2.

Answer:

Question 3.

Answer:

Distinguish between the following:

Question 1.
Proton and Neutron:
Answer:

Question 2.
Neutron and Electron:
Answer:

Question 3.
Proton and Electron:
Answer:

Question 4.
Atomic number and Atomic mass number:
Answer:

Answer the following questions in one sentence each:

Question 1.
Name the particles which are present in the nucleus of an atom.
Answer:
Protons and neutrons are present in the nucleus of an atom.

Question 2.
State the relation between the number of protons, the number of neutrons and the atomic mass number (A) of an element.
Answer:
Atomic mass = Number of + Number of number (A) protons (p) neutrons (n)

Question 3.
Chlorine contains 17 protons and 18 neutrons. What is its atomic mass number?
Answer:
The atomic mass number of chlorine is 35.

Question 4.
Carbon contains 6 protons and 6 neutrons. State its atomic number and atomic mass number.
Answer:
The atomic number of carbon is 6 and the atomic mass number is 12.

Question 5.
State one use of isotopes of cobalt.
Answer:
Isotopes of Cobalt-60 are used in the treatment of cancer.

Question 6.
State one use of isotopes of i uranium.
Answer:
Isotopes of uranium are used for production of electrical energy.

Question 7.
Write the electronic configuration of oxygen.
Answer:
Electronic configuration of oxygen is 2, 6.

Question 8.
Write the electronic configuration of chlorine.
Answer:
Electronic configuration of chlorine is 2, 8, 7.

Question 9.
State the number of electrons in the L shell of lithium.
Answer:
There is one electron in the L shell of lithium.

Question 10.
State the number of electrons in the M shell of argon.
Answer:
There are 8 electrons in the M shell of argon.

Question 11.
State the number of electrons in the K shell of helium.
Answer:
There are two electrons in the K shell of helium.

Question 12.
Name isotopes of hydrogen.
Answer:
Hydrogen, Deuterium and Tritium are the isotopes of hydrogen.

Question 13.
Name two isotopes of carbon.
Answer:
[latex]{ }_{6}^{12} \mathrm{C}\) and \({ }_{6}^{14} \mathrm{C}\) are the isotopes of carbon.

Question 14.
Name two elements in which the K and L shells of an atom are completely filled with electrons.
Answer:
The elements are neon and argon.

Question 15.
From the symbol \({ }_{8}^{16} \mathrm{O}\), state the electronic configuration of oxygen and the atomic mass number of isotope oxygen.
Answer:
Electronic configuration of oxygen : 2, 6. Atomic mass number of oxygen : 16.

Question 16.
The atomic mass number of an element is 18, and the element contains 8 electrons. What is the number of protons and neutrons in it?
Answer:
Number of protons : 8, Number of neutrons : 10.

Question 17.
An atom contains 2 protons, 2 electrons and 3 neutrons. State its atomic number and atomic mass number.
Answer:
Atomic number: 2, Atomic mass number: 5.

Question 18.
How many electrons could there be in the outermost orbit of an element whose valency is 3?
Answer:
If the valency of an element is 3 then there is a possibility of 3 or 5 electrons in the outermost orbit.

Question 19.
Which element is used as fuel in atomic reactors?
Answer:
Isotopes of uranium are used as fuel in atomic reactors.

Question 20.
Name the place and the first nuclear reactor in India.
Answer:
Apsara at Bhabha Atomic Research Centre in Mumbai is the first nuclear reactor in India.

Answer the following questions:

Question 1.
Explain Dalton’s atomic theory.
OR
Write the postulates of Dalton’s atomic theory.
Answer:
Dalton’s atomic theory:

1. According to Dalton’s atomic theory matter is made up of atoms and atoms are indivisible and indestructible.
2. All atoms of an element are alike while different element have different atom with different mass.

Try this:

Question a.
Take a solid ball and a Bundi Laddu. Press both these spheres with your palms. What did you find?
Answer:
Solid ball does not break and Bundi Laddu breaks into pieces if you press hard.

Question b.
Cut the solid ball with a sharp knife. What did you find?
Answer:
There is no cavity inside the ball.

Question 2.
How will you think about atomic mass distribution according to Thomson’s I model? Whether this distribution is uniform or non uniform as per Dalton’s atomic theory?
(Use your brainpower!
Answer:
In Thomson’s model the distribution of atomic mass is uniform. Dalton’s atomic theory does not say anything about atomic mass distribution.

Question 3.
If the striker flicked by you misses the coin that you aimed at, where would the striker go?
Can you tell?
Answer:
The striker will continue to move practically with the same velocity till it strikes some other coin or the edge of the board or enter the pocket.

Question 4.
If the striker hits the coin, in which direction would it go? Straight forward to a side or in the reverse direction?
Answer:
Striker may go straight forward or it may be deflected depending upon the exact direction of the motion of the striker.

Question 5.
Draw a neat labelled diagram of Thomson’s atomic model.
Answer:

Question 6.
What were the conclusions drawn from the alpha particle experiment performed hy Rutherford?
Answer:
On the basis of the alpha particle experiment the following conclusions were drawn by Rutherford:

1. An atom has tiny, dense positively charged nucleus at centre of an atom.
2. Most of the mass of the atom is concentrated in the nucleus.
3. Negatively charged particles called electrons revolve around the nucleus.
4. The total negative charge on all the ; electron is equal to the positive charge on ‘ the nucleus. As the opposite charges are balanced, the atom is electrically neutral.
5. There is an empty space between the i revolving electron and the atomic nucleus.

Question 7.
Explain Rutherford’s atomic model.
Answer:

1. An atom has tiny, dense, positively charged core called the nucleus.
   
2. Most of the mass of the atom is concentrated in the nucleus.
3. Electrons bear negative charge. They revolve around the nucleus in orbits.
4. The structure of an atom may be regarded as a miniature of the solar system, the nucleus as the sun and the electrons as the planets.

Question 8.
Which discovery did point out that an atom has internal structure?
(Use your brainpower!
Answer:
The discovery of radioactivity (1896) pointed out that an atom has internal structure.

Question 9.
What is the difference between the solid atom in Dalton’s atomic theory and Thomson’s atomic model?
(Use your brain power!
Answer:
The solid atom in Dalton’s atomic theory is a single particle it does not have any structure and also does not have any constituents. In Thomson’s model, atom is made of positive and negative charges. Thus it is not a single particle. It has constituents and has internal structure.

Question 10.
Explain the difference between the distribution of positive charge in Thomson’s atomic model and Rutherford’s atomic model.
(Use your brain power!
Answer:
According to Thomson’s atomic model, the atom is a homogeneous sphere of positive charge. According to Rutherford’s atomic model, the positive charge is concentrated in the nucleus.

Question 11.
What is the point difference between the place of electron in the atomic models of Thomson and Rutherford?
(Use your brain power!
Answer:
According to Thomson’s atomic model, the negatively charged electrons are embedded in a gel of positive charge and they are stationary. According to Rutherford’s atomic model, the negatively charged electrons revolve around the nucleus.

Question 12.
What is the thing which is present in Rutherford’s atomic model and not present in Dalton’s and Thomson’s atomic models?
(Use your brain power!
Answer:
1. Dalton’s atomic model:
Dalton’s atomic theory does not tell anything about the structure of the atom. There is no mention of electron in Dalton’s atomic theory.

Rutherford’s atomic model:
Rutherford’s atomic model tells about the structure of the atom, i.e. the electron revolving around the nucleus.

2. Thomson’s atomic model:
The electrons are embedded in a gel of positive charge. Here the electrons are stationary and there is no concept of nucleus.

Rutherford’s atomic model:
In Rutherford’s atomic model, the electrons are not stationary, they revolve around the nucleus which is positively charged.

Question 13.
Explain Niels Rohr’s atomic model.
OR
Write the postulates of Bohr’s atomic model.
Answer:
The important postulates of Bohr’s atomic model are as follows:

1. The electrons revolving around the atomic nucleus lie in the concentric circular orbits at certain distance from the nucleus.
2. Energy of an electron is constant while it is in a particular orbit.
3. When an electron jumps from an inner orbit to an outer orbit it absorbs specific amount of energy, and when it jumps from an outer orbit to an inner orbit it emits specific amount of energy.
4. The energy emitted or absorbed during these transitions is equal to energy difference between the initial state and the final state of the electron.

Question 14.
How many types of subatomic particles are found in atom?
Use your brainpower!
Answer:
There are three types of subatomic particles found in atom, viz. the proton, neutron and electron.

Question 15.
Which subatomic particles are electrically charged?
Use your brain power!
Answer:
The proton is a positively charged subatomic particle and the electron is a negatively charged particle.

Question 16.
Which subatomic particles are present in the nucleus?
Use your brain power!
Answer:
The proton and neutron are present in the nucleus.

Question 17.
Where are electrons revolving around the nucleus placed?
Use your brain power!
Answer:
Electrons revolve in the discrete orbits around the nucleus.

Question 18.
State the characteristics of the neutron.
Answer:

1. The neutron is electrically neutral and is denoted by the symbol ‘N’.
2. It is present in the nucleus along with the proton.
3. The mass of the neutron is almost equal to lu which is almost equal to that of the proton.

Question 19.
State the characteristics of protons.
Answer:

1. Protons are positively charged particles and are denoted by the symbol ‘P’.
2. They are present in the nucleus of an atom.
3. The mass of the proton is very nearly equal to lu which is almost equal to that of the hydrogen atom.
4. All the elements contain protons.

Question 20.
State the characteristics of electrons.
Answer:

1. Electrons are negatively charged particles and are denoted by the symbol ‘e’.
2. They have negligible mass.
3. They revolve around the nucleus in certain discrete orbits.
4. In an atom, the number of electrons is equal to the number of protons in its nucleus (Z).

Question 21.
The symbol used for oxygen is ‘O’. There are 8 protons and 8 neutrons in its nucleus. From this determine the 1 atomic number (Z) and mass number (A) of oxygen and arrange these in a 1 conventional symbol.
Use your brain power!
Answer:
Atomic mass number
= Protons + Neutrons
= 8 + 8
Atomic mass number = 16
Atomic number, i.e. the proton number = 8
The conventional symbol = \(\mathrm{A} \mathrm{O}\)
Z = Atomic number
i.e. number of protons is 8.
A = Atomic mass number = 16.
The conventional symbol = \({ }_{8}^{16} \mathrm{O}\).

Question 22.
Atomic number of carbon is 6. How many electrons are there in a carbon atom?
Use your brainpower!
Answer:
The atomic number of carbon, i.e. the proton number of carbon is 6.
The number of electron in the extranuclear part is equal to the number of protons in the nucleus.
∴ The number of electrons in a carbon atom = 6.

Question 23.
A sodium atom contains 11 electrons. What is the atomic number of sodium?
Use your brain power!
Answer:
The number of electron in the extranuclear part is equal to the number of protons, i.e. atomic number. The atomic number of sodium is 11.

Question 24.
The atomic number and mass number of magnesium are 12 and 24 respectively. How will you show this by the convention symbol?
Use your brainpower!
Answer:
The atomic number, atomic mass number and the symbol of an element are written as:

\({ }_{12}^{24} \mathrm{Mg}\) the conventional symbol for magnesium.

Question 25.
The atomic number and mass number of calcium are 20 and 40 respectively. Deduce the number of neutron present in the calcium nucleus.
Use your brain power!
Answer:
There are 20 neutrons in the nucleus of calcium.
[Note: The number of neutrons N = A – Z = 40 – 20 = 20]

Question 26.
Write a note on distribution of electrons in orbits.
OR
What is the maximum number of ( electrons that can be accommodated in each of the orbits (shells) K, L, M, N, etc.?
Answer:
The number of maximum electrons in different orbits of the atom are fixed. The orbit (shell) closest to the nucleus is: given the number 1, the next orbit the ; number 2… etc. The orbits one are designated ; by letters K, L, M, N,… corresponding to the shell numbers n = 1, 2, 3, 4, … etc. The maximum number of electrons in a given orbit is 2n², when n is the number of orbit (shell), thus the first shell has the capacity of 2 electrons, the second 8, the third 18, the fourth 32 and so on. The electrons in the K shell have minimum energy. The electrons in the subsequent shells possess higher energy.

Question 27
There is a similarity in atomic structure and solar system. The planets revolve around the sun due to the gravitational force. Which force might be acting in the atomic structure?
Can you tell?
Answer:
The electric force might be acting in the atomic structure. In the atomic structure, electric force is much stronger than gravitational force.
[Note: Here the gravitational force is very very small compared to the electric force, therefore, the gravitational force can be ignored.]

Question 28.
Positively charged proton are together in the nucleus. What might be, one of the function of the neutrons in the nucleus?
Can you tell?
Answer:
One of the function of the neutrons in the nucleus is to keep the protons and neutrons together by nuclear force.

Question 29.
What do you understand by electronic configuration?
Answer:
The shellwise distribution of the electron in an atom of an element is called the electronic configuration.?

Question 30.
Write the electronic configuration of the following elements:
(1) Hydrogen, (2) Magnesium. (3) Aluminium, (4) Phosphorus, (5) Sulphur.
Answer:

Question 31.
Use the following molecular formulae to determine the valencies of H, Cl, O, S, N, C, Br, I, Na.
Molecular formulae – H₂, HCl, H₂O, H₂S, NH₃, CH₄, HBr, HI, NaH.
Can you recall?
Answer:

Question 32.
Draw suitable diagrams to show the electronic configuration of the atoms of the following elements: Hydrogen, helium, carbon, neon, sodium, chlorine.
Answer:

Question 33.
What are the symbols used for the shells which accommodate the electrons in various atoms?
Use your brain power!
Answer:
The symbols used for the shells which accommodate the electrons are K, L, M, N, … respectively.

Question 34
What is the symbol and ordinal number of the innermost shell?
(Use your brain power!
Answer:
The symbol of the innermost shell is K and ordinal number of the innermost shell is 1.

Question 35.
Write symbol of electron distribution in shell of fluorine atom?
Use your brain power!
Answer:
Symbol for fluorine atom = F,
Electronic configuration of fluorine \(\begin{array}{l}\mathrm{K} \\2\end{array}\), \(\begin{array}{l}\mathrm{L} \\7\end{array}\).

Question 36.
Which is the outermost shell of fluorine atom?
Use your brain power!
Answer:
The outermost shell of fluorine atom is L.

Question 37.
Which is the outermost shell of sodium atom?
Use your brain power!
Answer:
The outermost shell of sodium atom is M shell.

Question 38.
Which is the outermost shell of hydrogen atom?
Use your brain power!
Answer:
The outermost shell of hydrogen is K shell.

Question 39.
What is meant by the atomic number (Z) of an element?
(Use your brain power!
Answer:
Atomic number (Z): The number of electrons or protons in an atom is called the atomic number. It is denoted by Z.

Question 40.
Atomic numbers (Z) of some elements are given here. Write down the number of electron present in the outermost shell of each of them.
Use your brain power!
Answer:

Question 41.
The number of electrons of some elements is given here. By using it write the electronic configuration, number of valence electron and valency of the respective elements.
Use your brain power!
Answer:

Question 42.
Why are the atomic numbers and atomic mass numbers always in whole numbers?
Use your brain power!
Answer:
The total number of protons and neutrons in the nucleus of the atom is called the atomic mass number (A). The number of electrons or protons in an atom is called the atomic number (Z). Both protons and neutrons are whole numbers, therefore, atomic numbers and atomic mass numbers are always in whole numbers.

Question 43.
Sulphur contains 16 protons and 16 neutrons. What would be its atomic number and mass number?
Use your brain power.
Answer:
The atomic number of sulphur is 16 and the atomic mass number is 32.

Question 44.
State the uses of isotopes.
Answer:
Isotopes of some elements are radioactive. Isotopes are used in various fields such as industry, agriculture, medicine, research field.

1. Isotopes of uranium is used for nuclear fission and production of electricity.
2. Cobalt – 60 are used in the treatment of cancer.
3. Iodine – 131 is used in the treatment of goitre.
4. The radioactive isotopes, Sodium – 24 are used for detection of cracks (leakage) in the underground pipes.
5. Radioactive isotopes are used for food preservation from microbes.
6. The radioactive C – 14 is used for determining the age of archaeological objects.

Question 45.
Write a note on nuclear reactor.
Answer:
1. A machine that generates electricity on large scale by using atomic energy is called a nuclear reactor. In a nuclear reactor, the nuclear energy in atom is released by bringing about nuclear reactions on the nuclear fuel.

2. When uranium – 235 is bombarded with a slow speed neutron, it undergoes nuclear fission. Various elements are produced. For example: Krypton – 92 and Barium – 141 along with 2 to 3 neutrons are emitted on fission, these neutron have high speed. Their speed is reduced and they are used for bombarding more Uranium – 235 nuclei.

The process is repeated many times. In this way a chain reaction of nuclear fission takes place (See the figure). A large amount of nuclear energy is released during a chain reaction of fission. The chain reaction is controlled to prevent the probable explosion.

Neutrons are slowed down using graphite or heavy water as moderator. The chain reaction is controlled by absorbing neutron with the help of rods of boron, cadmium and beryllium. The heat produced in the fission is taken out by water as coolent. Water is converted into steam. The available heat is used to drive turbines to produce electricity.

Give scientific reasons:

Question 1.
In Rutherford’s experiment, some alpha particles colliding with the thin gold foil are turned back.
Answer:
1. All the positive charges in an atom is concentrated in a very small region at the centre of the atom. This region is called the nucleus. Electrons revolve around the nucleus, but most of the atom is empty. Alpha particles are positively charged.

2. When a thin sheet of gold is bombarded by alpha particles, most of the particles pass through it without deviation as the atom is almost empty. But some alpha particles move directly towards the positive nuclei, collide with them and due to the electric repulsion, turn back. Thus, in Rutherford’s experiment, some alpha particles colliding with the thin gold foil are turned back.

Question 2.
Two electrons in helium atom are placed in only one shell while three electrons in lithium atom occupy two shells.
Answer:
1. The electronic configuration of helium is (2). It indicates that helium atom has two electrons. Both the electrons are accommodated in the K shell. The maximum capacity of the K shell is two electrons and is maintained in all the elements. Hence, two electrons in helium are placed in only one shell.

2. The electronic configuration of lithium is (2, 1). It indicates that lithium atom has three electrons. The first shell K accommodates two electrons, i.e., the maximum capacity of the K shell. The remaining electron is accommodated in the next shell, i.e., the L shell. Thus, three electrons in lithium occupy two shells (K and L).

Complete the following:

Question 1.
Complete the table by putting tick mark in appropriate box.
Answer:
Types of substances:

Question 2.
Complete the table:
Answer:

Write the maximum number of electron in a shell using the above table. K Shell : 2, L Shell : 8, M Shell : 18, N Shell : 32.

Question 3.
Complete the table:
Answer:
Electronic configuration of some elements:

Question 4.
Complete the following table:
Answer:
Relationship between valency and electronic configuration:

Question 5.
In table 4 column you have written of that element? How many electrons identified valency from its molecular are used to complete the octet? formulae. When the number of the valency electrons in an element ‘x’ is 4 or less than 4, does ‘x’ match with the valency of that element?
Use your brain power!
Answer:
When the number of the valence electrons in an element x is 4 or less than 4, then x matches with the valency of that element.

Question 6.
When the number of the valence electrons in an element ‘x’ is 4 or more than 4, does’(8 – x)’ match with the valency of that element? How many electrons are used to complete the octet?
(Use your brain power!
Answer:
When the number of the valence electrons in an element x is 4 or more than 4, then (8-x) matches with the valency of that element. (8-x) electrons are used to complete the octet.

Question 7
Complete the table:
Answer:

Balbharati Maharashtra State Board 8th Std Science Textbook Solutions 

• Living World and Classification of Microbes Class 8 Science Textbook Solutions
• Health and Diseases Class 8 Science Textbook Solutions
• Force and Pressure Class 8 Science Textbook Solutions
• Current Electricity and Magnetism Class 8 Science Textbook Solutions
• Inside the Atom Class 8 Science Textbook Solutions
• Composition of Matter Class 8 Science Textbook Solutions
• Metals and Nonmetals Class 8 Science Textbook Solutions
• Pollution Class 8 Science Textbook Solutions
• Disaster Management Class 8 Science Textbook Solutions
• Cell and Cell Organelles Class 8 Science Textbook Solutions

Std 6 Science Chapter 9 Motion and Types of Motion Question Answer Maharashtra Board

Balbharti Maharashtra State Board Class 6 Science Solutions Chapter 9 Motion and Types of Motion Notes, Textbook Exercise Important Questions and Answers.

Class 6 Science Chapter 9 Motion and Types of Motion Question Answer Maharashtra Board

1. Identify the types of motion.

Question a.
Movement of the earth around the sun: …………… .
Answer:
periodic, drcular

Question b.
Movement of ceiling fan: …………… .
Answer:
circular

Question c.
A rocket launched from the ground: ……….. .
Answer:
linear

Question d.
A fish swimming in water: ……… .
Answer:
random

Question e.
The plucked string of a sitar:………….. .
Answer:
oscillatory motion

2. Fill in the blanks.
(linear, non-linear, uniform linear, non-uniform linear, uniform circular, random, circular, non-uniform circular)

Question a.
If a ball is released from the terrace of a building, it comes down in ………… motion. On the other hand, it reaches the ground in ………… motion if it is thrown with a force away from the terrace in a direction parallel to the terrace.
Answer:
uniform linear, non-uniform linear

Question b.
The motion of an aeroplane on the runway before take off is …………. .
Answer:
linear

Question c.
The kite looking for its prey flies with …………. motion in the sky.
Answer:
circular

Question d.
Children sitting in a rotating giant wheel have ………. motion, while those sitting in a merry-go-round have a ………. motion.
Answer:
uniform circular, non-uniform circular

3. How are we different?.

Question a.
Oscillatory motion and Linear motion.
Answer:

Question b.
Linear motion and Random motion
Answer:

Question c.
Random motion and Oscillatory motion
Answer:

4. Explain in your own words, giving one example each.

Question a.
Linear motion
Answer:
An object that shows displacement along a straight line is called linear motion, e.g. A vehicle moving on a road.

Question b.
Oscillatory motion
Answer:
The motion of a body swinging back and forth is called oscillatory motion, e.g. Motion of a pendulum of a clock.

Question c.
Circular motion
Answer:
The motion of an object along a circular path is called circular motion, e.g. Motion of a ceiling fan.

Question d.
Random motion
Answer:
The motion that changes its direction and speed continuously is called random motion, e.g. Motion of a butterfly.

Question e.
Periodic motion
Answer:
The repetitive motion in which the moving object passes through a certain point again and again after a fixed period is called as periodic motion, e.g. The minute hand of a clock.

5. Answer the following questions in your own words. 

Question a.
Which types of motion are seen in birds flying in the sky?
Answer:

1. The birds flying in the sky exhibit random motion.
2. The wings of the birds show oscillatory motion.

Question b.
Write in detail about your experience of various types of motion while riding a bicycle on a road.
Answer:

1. The cycle itself shows linear motion.
2. The wheels of the cycle show circular motion.
3. The cycle chain shows periodic motion, if the speed is uniform.
4. The handle bar shows random motion.

6. Complete the puzzle using words for types of motion: 

Question a.
Complete the puzzle using the words for types of motion.
1. A spring is stretched and one end is released.
2. A minute hand.
3. A see-saw.
4-5.  Children in a march past.
6. A stone rolling down a hillside.

Answer:

1. Oscillatory
2. Circular
3. Periodic
4. Uniform
5. Linear
6. Random

Activity:

Question 1.
Make a list of various moving objects in the environment, and discuss the types of motion seen in them.

Class 6 Science Chapter 9 Motion and Types of Motion Important Questions and Answers

Identify the types of motion.

Question 1.
The movement of a see-saw.
Answer:
oscillatory motion

Question 2.
The motion of a moving ant.
Answer:
random

Question 3.
The marching army soldiers.
Answer:
linear

Question 4.
A train approaching a station.
Answer:
non-uniform linear

Question 5.
A meteor falling from the sky.
Answer:
linear

Fill in the blanks with suitable words from those given in the bracket:
(linear, non-linear, uniform linear, non-uniform linear, uniform circular, random, circular, non-uniform circular)

Question 1.
The motion that changes its speed and direction continuously is called ………. .
Answer:
random

Choose the correct alternative:

Question 1.
A baby is crawling. The motion is said to be …………….. .
(a) linear
(b) periodic
(c) circular
(d) random
Answer:
(d) random

Question 2.
The children are having a 50m running race. The motion exhibited is ………….. motion.
(a) linear
(b) periodic
(c) random
(d) circular
Answer:
(a) linear

Question 3.
The motions of the hands of a clock are ………….. and …………. .
(a) periodic, linear
(b) periodic, circular
(c) non-linear, non-uniform
(d) circular, non-uniform
Answer:
(b) periodic, circular

Question 4.
The motion of a pendulum of a clock is ……………. .
(a) linear
(b) oscillatory
(c) circular
(d) random
Answer:
(b) oscillatory

Question 5.
The motion of a butterfly from one flower to another flower is an example of …………… motion.
(a) circular
(b) periodic
(c) linear
(d) random
Answer:
(d) random

Question 6.
The distance traversed by an object in a unit time is called ……….. of that object.
(a) length
(b) motion
(c) speed
(d) displacement
Answer:
(c) speed

Explain it in your own words, giving one example of each.

Question 1.
Uniform linear motion
Answer:
When the distance traversed by an object along a straight line in unit time is the same, the motion is called as uniform linear motion, e.g. Motion of soldiers on parade.

Question 2.
Non-uniform linear motion
Answer:
When the distance traversed by an object along a straight line in unit time keeps on changing, the motion is called non-uniform linear motion.
e.g. A girl coming down a slide.

Question 3.
Non-linear motion
Answer:
The motion of an object that does not move in a straight line is called non-linear motion.
e.g. Motion of a swing,

Question 4.
Speed
Answer:
The distance traversed by an object in unit time is called the speed of that object.
e.g. A boy riding on a bicycle covers a distance of 15 kilometres in 3 hours.
Hence Speed = \(\frac{15}{3}\) = 5 kilometres/hour

Answer the following:

Question 1.
In which muscial instruments can you see oscillatory motion?
Answer:
Vibrating diaphragm of tabla, drum, dhol and strings of sitar, guitar show oscillatory motions.

Question 2.
With reference to types of motion, complete the table below.

Answer:

1. Non-linear
2. Uniform
3. Oscillatory
4. Periodic
5. Random.

Read the following stories and answer the questions.

Rita and Geetha are friends travelling from Mumbai to Pune. Seetha had come to the station to see her friends off. After 15 minutes train starts moving. Rita and Geetha feel that Seetha and the vendors on platform are moving backwards. Whereas, Seetha feels that Rita and Geetha are moving forward. Rita feels Geetha is not in motion and Geetha also feels Rita is not in motion. Can you say why?

Question a.
Are Rita and Geetha in motion?
Answer:
Rita and Geetha are not in motion as far as each other are concerned, as no displacement takes place. Both are in a train. For Seetha, both of them are in motion.

Question b.
Are the vendors and Seetha in motion?
Answer:
No, the vendors and Seetha are not in motion. But Rita and Geetha feel as if they are moving backwards.

Question c.
What can you conclude from this passage?
Answer:
An object which is in motion for one person may not be in motion for another. This shows that motion is relative.

Observe and discuss:

Question 1.
Observe the figure and classify the type of motion.


Answer:

1. Circular motion
2. Linear motion
3. Circular motion
4. Linear motion
5. Oscillatory motion
6. Oscillatory motion
7. Circular motion
8. Circular motion
9. Bird – Random; Wings – Oscillatory motion
10. Circular motion
11. Linear, circular

Can you tell?

Question 1.
While chasing a butterfly in a garden, do you run along a definite path or in the same direction all the time?
Answer:
No, we move in random motion.

Maharashtra State Board Class 6 Science Textbook Solutions

• Natural Resources – Air, Water and Land Class 6 Science Textbook Solutions
• The Living World Class 6 Science Textbook Solutions
• Diversity in Living Things and their Classification Class 6 Science Textbook Solutions
• Disaster Management Class 6 Science Textbook Solutions
• Substances in the Surroundings – Their States and Proper Class 6 Science Textbook Solutionsties
• Substances in Daily Use Class 6 Science Textbook Solutions
• Nutrition and Diet Class 6 Science Textbook Solutions
• Our Skeletal System and the Skin Class 6 Science Textbook Solutions
• Motion and Types of Motion Class 6 Science Textbook Solutions
• Force and Types of Force Class 6 Science Textbook Solutions

Std 8 Science Chapter 11 Human Body and Organ System Question Answer Maharashtra Board

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 11 Human Body and Organ System Notes, Textbook Exercise Important Questions and Answers.

Class 8 Science Chapter 11 Human Body and Organ System Question Answer Maharashtra Board

Class 8 Science Chapter 11 Human Body and Organ System Textbook Questions and Answers

1. Find out my partner.

Question a.

Answer:

2. Complete the following table.

Question a.

Answer:

3. Draw neat and labeled diagrams. 

Question a.
Respiratory system.
Answer:

Question b.
Internal structure of heart.
Answer:

4. Explain with reasons.

Question a.
Human blood is red coloured.
Answer:
The red colour of human blood is due to hemoglobin which is a red coloured conjugated protein with iron that is present on the red blood cells. Therefore, it looks red.

Question b.
Upward and downward movement of diaphragm occurs consecutively.
Answer:
The breathing movements are possible due to contraction and relaxation of the diaphragm. The rib muscles also help in these movements. When the ribs rise and diaphragm is lowered at the same time, then there is a decrease in pressure on lungs.

This causes movement of air into the lungs at the time of inhalation. On the other hand, when ribs come back to their normal position and diaphragm is risen, then pressure on the lungs increases. This causes movement of the air out of the body through the nose in the form of exhalation. These movements are possible only due to consecutive upward and downward movement of the diaphragm.

b

Question c.
Blood donation is considered to be superior of all donations.
Answer:
Blood cannot be manufactured by any artificial chemical process. The only way to obtain blood is by donations of blood from a live donor. Blood is needed at times of emergency. The life of person can be saved if timely blood transfusion is given to the needy victim or a patient. Since such donation can save a valuable human life, it is called superior of all donations.

Question d.
Person with ‘O’ blood group is considered as ‘universal donor’.
Answer:
Person with ‘O’ blood group does not have any antigen on his/her RBCs. The ‘O’ type blood thus cannot cause clotting reactions in the body of the recipients. Such persons with ‘O’ blood group can donate blood to any person having any blood group therefore they are considered as ‘universal donor’.

Question e.
Food must have limited amount of salts.
Answer:
More salt in diet means more sodium ions. These extra sodium salts cause rise in blood pressure. Such condition is called hypertension. This condition can be dangerous and fatal in some cases. Therefore, one must keep control over sodium content of the food.

5. Answer the following questions in your own words.

Question a.
Explain the functional correlation of circulatory system with respiratory, digestive and excretory system.
Answer:
1. Three systems viz. respiratory, digestive and circulatory always work in coordination.
2. Digestive system helps in breaking down complex food molecules into simple soluble nutrients at the end of the digestion process.
3. The soluble nutrients are absorbed in the circulating blood in the villi of the intestine.
4. The blood carries these nutrients to each cell during its circulation.
5. The respiratory system helps the oxygen from the air to be absorbed in the blood.
6. This process takes place in alveolus present in lungs. The oxygen is absorbed in the blood and through haemoglobin it is taken to every cell of the body. At the same time the unwanted carbon dioxide produced in each cell is given out in a process of gaseous exchange.
7. The soluble nutrients, and chiefly glucose is metabolized with the help of oxygen-producing energy. Thus, all the three systems bring about coordinated functions to keep the body alive.

Question b.
Explain the structure and function of human blood.
Answer:
I. Structure, i.e. components of the human blood: Human blood is a fluid connective tissue consisting of blood plasma and blood corpuscles suspended in it.

1. Plasma: Plasma is the fluid part of the blood which is pale yellow in colour. It is slightly alkaline in nature. It has 90-92% water, 6-8 % proteins and 1-2 % inorganic salts.
It contains proteins such as albumin, globulin, fibrinogen, etc. There are inorganic ions such as Ca, Na and K.

2. Blood cells:
a. Blood cells are mainly of three types, viz. RBCs, WBCs and blood platelets. They are produced in the red bone marrow.
b. RBCs are small, circular and enucleated cells. They are full of haemoglobin which is essential in transporting oxygen. RBCs are red blood cells which are 50 to 60 lakh per cubic millimetre. Their life span is 100 to 127 days.
c. WBCs are large, nucleated and colourless. They are of five subtypes, viz. neutrophils, basophils, eosinophils, monocytes and lymphocytes. They are 5 to 10 thousands per millimetre of blood.
d. Platelets are very small disc-shaped blood cells which are 2.5 to 4 lakh per cubic millimetre of blood.

II. Function of human blood:

1. Transport functions:

• Gases: Oxygen is carried via blood from lungs to cells in various parts of body and carbon dioxide from tissues to lungs.
• Nutrients: Simple nutrients like glucose, amino acids, fatty acids are taken up by blood from wall of alimentary canal and transported up to each cell in the body.
• Waste materials: Nitrogenous wastes like ammonia, urea, creatinine are released by tissues into blood which carries those to kidney for excretion.
• Enzymes and hormones: Blood transports the enzymes and hormones from the site of their production to the site of their action.

2. Protection: Antibodies are produced in the blood and they protect the body from microbes and other harmful particles.
3. Thermoregulation: Body temperature is maintained constant at 37 °C by vasodilation and vasoconstriction.
4. Maintaining the balance of minerals like Na, K in the body.
5. If bleeding occurs at the injury, platelets and a protein called fibrinogen of the blood form a clot and seal the injury.
6. Functions of blood cells:

• RBCs: With haemoglobin it carries out transport of respiratory gases.
• WBCs: Soldiers of the body. Produce antibodies and give immunity to body.
• Platelets: Help in blood clotting.

Question c.
Explain the importance and need of blood donation.
Answer:
Blood can never be synthesized artificially. There is no substitute for natural blood. Every healthy person possesses about 5 litres of blood in his or her body. In case of haemorrhage i.e. blood loss, the blood volume may reduce which can result into threat to life. Moreover, the loss of blood should be immediately taken care of, otherwise it may cost the life.

Therefore blood transfusion is very crucial in case of victims of accidents, patients of surgeries or mothers who suffer from blood loss during childbirth (parturition). Some diseases such as thalassemia, blood cancer, etc. also need regular transfusions. Therefore, blood is always needed in many such conditions. Blood donation is only option for such transfusions.

6. Explain the differences.

Question a.
Arteries and veins.
Answer:

Question b.
External and internal respiration.
Answer:

7. Which health parameters of blood donor should be checked? 

Question a.
Which health parameters of blood donor should be checked?
Answer:
Blood donor should be healthy. He or she should have good haemoglobin’s content. The RBC and WBC count should also be normal. They should not carry any parasites in their blood such as malarial parasite or dengue virus. The donor should not be HIV positive or should not have any infectious diseases. He should not have any addictions such s drug-abuse or alcohol consumption.

8. Fill in the blanks using appropriate words given in the bracket.
(hemoglobin, alkaline, diaphragm, red bone marrow, acidic, voluntary, involuntary,)

Question a.
RBCs of the blood contain ……….., an iron compound.
Answer:
RBCs of the blood contain haemoglobin, an iron compound.

Question b.
……………….. is present between thoracic and abdominal cavity.
Answer:
Diaphragm is present between thoracic and abdominal cavity.

Question c.
Cardiac muscles are …………… .
Answer:
Cardiac muscles are involuntary.

Question d.
pH of oxygenated blood is …………… .
Answer:
pH of oxygenated blood is alkaline.

Question e.
Production of RBCs occurs in ……………… .
Answer:
Production of RBCs occurs in red bone marrow.

8. Find odd one out.

Question a.
A, O, K, AB, B.
Answer:
K (All others are blood groups.)

Question b.
Blood plasma, platelets, blood transfusion, blood corpuscles.
Answer:
Blood transfusion (All others are components of blood.)

Question c.
Trachea, alveoli, diaphragm, capillaries.
Answer:
Capillaries (All others are parts of respiratory system. Capillaries exist throughout the body.)

Question d.
Neutrophils, globulins, albumins, prothrombin.
Answer:
Neutrophils (All others are proteins present in the plasma.)

10. Read the following paragraph and identify the disease.

Today, her child became one and half year old. However, that child does not seem to be healthy and happy. It was continuously crying and gradually becoming weak. It has shortness of breath. Its nails have become blue.
Answer:
The heart of the child is not functioning properly. Bluish nails show lack of oxygen, thus the baby may be suffering also from respiratory problems.

11. Your neighboring uncle has been diagnosed with hypertension. What should he do to keep his blood pressure within normal range?

Question a.
Your neighboring uncle has been diagnosed with hypertension. What should he do to keep his blood pressure within normal range?
Answer:
Hypertension has many causes. Try to find out what is the exact cause. Is it lack of exercise, obesity, lots of fast and junk food consumption, over-intake of salt, mental tension, etc. He should visit a proper physician and take prescribed blood pressure control medicines. He should never miss a single tablet. He should avoid salty and preserved food. He should practice yoga and meditation. He should also undertake some stress- management techniques.

Project:

Question a.
Collect information about various modern treatments on heart diseases.

Class 8 Science Chapter 11 Human Body and Organ System Important Questions and Answers

Rewrite the statements after correcting them:

Question 1.
Cells need supply of insoluble nutrients and oxygen for the energy production.
Answer:
Cells need the supply of soluble nutrients and oxygen for the energy production.

Question 2.
Respiratory system and respiration begins with mouth.
Answer:
Respiratory system and respiration begins with nose.

Question 3.
A lung is present on either sides of heart in abdominal cavity.
Answer:
A lung is present on either sides of heart in thoracic cavity.

Question 4.
Continuous upward and downward movement of diaphragm is necessary to bring about the beating of heart.
Answer:
Continuous upward and downward movement of diaphragm is necessary to bring about the breathing.

Question 5.
Blood vessels which carry the blood away from heart are called veins.
Answer:
Blood vessels which carry the blood away from heart are called arteries.

Question 6.
William Harvey described the blood groups in man.
Answer:
William Harvey described the mechanism of circulation in the body.

Question 7.
Capillaries unite together to form the arteries.
Answer:
Capillaries unite together to form the veins.

Match the columns/Find out my partner:

Question 1.

Answer:

Complete the following table:

Question 1.

Answer:

Define the following terms:

1. Inhalation: Inhalation is taking in air through the nose from the surrounding
2. Exhalation: Exhalation is giving out the air back to the outer environment.
3. External respiration: The processes of inhalation and exhalation both together are called external respiration.
4. Internal respiration: Exchange of gases between cells and tissue fluid is called internal respiration.
5. Cellular respiration: Production of energy in the form of ATP from oxidation of glucose and other soluble nutrients is called cellular respiration.
6. Thermoregulation: Maintenance of the body temperature to a constant level by performing vasoconstriction or vasodilation is called thermoregulation.
7. Blood pressure: Pressure exerted by the flowing blood on the blood vessel wall is called blood pressure.
8. Systolic pressure: The maximum blood pressure exerted by the flowing blood when the heart is contracting is called systolic pressure.
9. Diastolic pressure: The minimum blood pressure exerted by the flowing blood when the heart is not contracting but receiving (i.e. relaxing) the blood is called diastolic pressure.
10. Hypertension or High Blood Pressure: The blood pressure value of 140 – 159 mm Hg which is more than the normal blood pressure is called hypertension or high blood pressure.
11. Sphygmomanometer: The instru¬ment used for measuring blood pressure is called sphygmomanometer.
12. Hematology: The branch of medical science in which the blood, haemapoietic organs (organs that produce blood cells) and blood disorders are studied is called haematology.

Answer the following questions in one or two sentences each:

Question 1.
What are the heart sounds and why are they produced?
Answer:
There are two types of heart sounds, one is ‘lubb’ and other is ‘dub’. These are produced due to closure of the heart valves.

Question 2.
What is blood circulation?
Answer:
The process of pumping the blood to all the parts of the body and bringing it back again to the heart is called the blood circulation.

Question 3.
Name any four proteins present in the blood plasma.
Answer:
The proteins present in the blood plasma are albumin, globulins, fibrinogen and prothrombin.

Question 4.
Which inorganic ions control the function of muscles and nerves?
Answer:
Calcium, sodium and potassium control the functions of muscles and nerves.

Question 5.
What is the basis on which blood group is determined?
Answer:
The antigen present on the RBCs: and the antibodies present in the plasma of I the blood determine the type of blood group. The genes of parents are responsible for the type of blood group that the child inherits.

Question 6.
Under which conditions, blood is required for donation?
Answer:
Whenever there is hemorrhage, the patient requires blood. Such patients are accident victims, those who excessively bleed, women during childbirth (parturition) and for patients undergoing surgeries.

Question 7.
How much blood is collected from a person during donation?
Answer:
About 350 ml of blood is collected from a person during donation.

Question 8.
When is National Voluntary Blood Donation Day observed?
Answer:
National Voluntary Blood Donation Day is observed on 1st October every year.

Explain the differences:

Question 1.
Atria and ventricles:
Answer:

Question 2.
RBCs and WBCs:
Answer:

Give scientific reasons:

Question 1.
A very large number of alveoli is present in lungs, which are covered over by capillary network.
Answer:
Due to very large number of alveoli the surface area of the lungs is increased many a times for the gaseous exchange. The alveoli are covered over by capillary network for rapid gaseous exchange. The oxygen is taken in the body and at the same time carbon dioxide is given out of the body only by the gaseous exchange occurring at the alveolar surface.

Question 2.
Heart is covered by double layered pericardial membrane.
Answer:
Pericardium is the protective double membrane that covers the heart. In between the two layers of this membrane there is protective fluid. The pericardium and the fluid together protect the heart from friction and mechanical shock. Since heart is a vital organ, it is well protected by such pericardial membrane.

Question 3.
Veins are provided with valves.
Answer:
Valves prevent the backflow of the blood. Blood in the veins is not under great pressure so it is likely that it may flow back. But valves prevent such movements. Therefore they are provided with valves.

Write short notes on the following:

Question 1.
Cellular respiration:
Answer:

1. During respiration, the glucose molecules along with some other soluble nutrients are slowly oxidized with the help of oxygen in each cell.
2. In this process the energy is released in the form of ATP, CO₂ and water vapours are produced.
3. These products are not needed for the body and hence given out of the body in exhalation.
4. This process of cellular respiration is shown by the following reaction:
   C₆H₁₂O₆ + 6O₂ = 6CO₂ + 6H₂O + Energy (38ATP)

Question 2.
Lung:
Answer:

1. Pair of lungs is the main respiratory organ in the human body. They are located in thoracic cavity.
2. They are present on either sides of heart.
3. Each lung has double layered pleural membranes.
4. Trachea bifurcates into two bronchi. Each bronchus enters lung on its side and S divide and re-divide into fine bronchioles.
5. At the end of each bronchiole there is alveolus. Alveolus is surrounded by capillary network.
6. Each alveolus is extremely thin walled and hence gaseous exchange can occur through diffusion here. Due to thousands of alveoli, the lung surface is increased many a times.
7. Deoxygenated blood coming from heart by pulmonary arteries is purified here in the lungs.
8. It is mixed with oxygen due to gaseous exchange and returned back to the heart by pulmonary veins. Lungs thus continuously help in oxygenation of blood with the help of all of the alveoli.

Question 3.
Diaphragm:
Answer:

1. Diaphragm is a muscular partition that divides the thoracic and abdominal cavity.
2. Located at the base of thoracic cage, it is very important in breathing movements.
3. Diaphragm can undergo consecutive upward and downward movements.
4. These movements along with movements of thoracic cage cause rise and fall of the pressure in the thoracic cavity.
5. Rising up of ribs and lowering of diaphragm causes the decrease in air pressure which makes the air to move into the lungs through nose. This is inhalation.
6. When the pressure rises in the thoracic cavity again, the air is given out. This is exhalation.
7. This is caused due to ribs returning to their original position and rising diaphragm. This simultaneously increases the pressure in thoracic cavity.

Question 4.
Structure of human heart:
Answer:

1. Human heart is four chambered muscular organ.
2. The size of the heart is about one’s own fist and its weight is about 360 gm.
3. For protection, it is covered over by double-layered pericardium.
4. The wall of the heart is made up of cardiac muscles which are involuntary in nature. They have the capacity of rhythmic beating.
5. The upper two chambers are called right and left atrium and lower two chambers are called right and left ventricle.
6. Between right atrium and right ventricle there is tricuspid valve which guards the opening. Similarly between left atrium and left ventricle there is bicuspid valve.
7. On entire right side of the heart there is deoxygenated blood.
8. On entire left side of the heart there is oxygenated blood.
9. Right atrium receives deoxygenated blood by superior and inferior vena cava. These two major veins bring deoxygenated blood from entire body to the heart.
10. Left atrium receives oxygenated blood from lungs by pulmonary vein.
11. Right ventricle sends the deoxygenated blood to lungs for oxygenation, through pulmonary artery.
12. Left ventricle supplies oxygenated blood to entire body through systemic aorta.

Question 5.
Human Blood Groups:
Answer:

1. The A, B, O blood group system is the most popular and medically important blood group system of human beings.
2. The blood group is determined due to antigenic protein present on the RBCs and the antibody present in the plasma.
3. The four main groups of human blood are A, B, AB and O.
4. According to the presence or absence of Rh antigen the blood groups are further said to be Rh-positive or Rh-negative.
5. This makes total eight blood groups which are taken into consideration at the time of blood transfusions.
6. Blood groups are dependent on genes and are thus hereditary in nature.

Answer the following:

Question 1.
How do the organisms like amoeba, earthworm, cockroach, plants, various aquatic animals, bird, respire? Prepare a chart.
Answer:

Diagram – based questions:

Question 1.
Sketch and label structure of alveolus showing gaseous exchange.
Answer:

Question 2.
Sketch and label artery and vein showing structural difference between the two.
Answer:

Question 3.
Draw a diagram to show formation of capillaries. Also show how capillaries form a vein.
Answer:

MCQs based on experiments:

I. Human respiratory system:

Question 1.
From which organ does respiratory system of man begin?
(a) Trachea
(b) Lungs
(c) Alveolus
(d) Nose
Answer:
(d) Nose

Question 2.
Which of the statement given below is correct?
(a) Wind pipe is present in front of food pipe.
(b) Food pipe is present in front of wind pipe.
(c) Wind pipe and food pipe are not near each other.
(d) Wind pipe is same as oesophagus and food pipe is called trachea.
Answer:
(a) Wind pipe is present in front of food pipe.

Question 3.
Which type of respiration includes inhalation and exhalation?
(a) Internal respiration
(b) External respiration
(c) Cellular respiration
(d) None of the above
Answer:
(b) External respiration

Question 4.
How many molecules of ATP are produced from one molecule of glucose ?
(a) 26
(b) 36
(c) 38
(d) 40
Answer:
(c) 38

Question 5.
Where is sound box located in the body?
(a) At the beginning of the wind pipe.
(b) At the beginning of the food pipe.
(c) At the end of the wind pipe.
(d) At the end of the food pipe.
Answer:
(a) At the beginning of the wind pipe.

II. Structure of heart:

Question 1.
What is the location of a bicuspid valve in human heart?
(a) Between right and left ventricle.
(b) Between left and right atrium.
(c) Between left atrium and left ventricle.
(d) Between right atrium and right ventricle.
Answer:
(c) Between left atrium and left ventricle.

Question 2.
Which blood vessels bring deoxygenated blood to the right atrium?
(a) Superior and inferior vena cava
(b) Pulmonary veins
(c) Pulmonary artery
(d) Systemic aorta
Answer:
(a) Superior and inferior vena cava

Question 3.
Which artery carries deoxygenated blood and which vein carries the oxygenated blood respectively?
(a) Dorsal aorta and inferior vena cava respectively.
(b) Pulmonary vein and pulmonary artery respectively
(c) Pulmonary artery and pulmonary vein respectively
(d) Superior vena cava and inferior vena cava respectively.
Answer:
(c) Pulmonary artery and pulmonary vein respectively

Question 4.
Under which of the following condition will rate of heartbeat be faster?
(a) Sleeping
(b) Resting
(c) Running
(d) Sitting
Answer:
(c) Running

Question 5.
Which chambers of the heart are called receiving chamber?
(a) Both atria
(b) Right ventricle
(c) Left ventricle
(d) Only left atria
Answer:
(a) Both atria

Balbharati Maharashtra State Board 8th Std Science Textbook Solutions

• Human Body and Organ System Class 8 Science Textbook Solutions
• Introduction to Acid and Base Class 8 Science Textbook Solutions
• Chemical Change and Chemical Bond Class 8 Science Textbook Solutions
• Measurement and Effects of Heat Class 8 Science Textbook Solutions
• Sound Class 8 Science Textbook Solutions
• Reflection of Light Class 8 Science Textbook Solutions
• Man-made Materials Class 8 Science Textbook Solutions
• Ecosystems Class 8 Science Textbook Solutions
• Life Cycle of Stars Class 8 Science Textbook Solutions

Std 8 Science Chapter 4 Current Electricity and Magnetism Question Answer Maharashtra Board

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 4 Current Electricity and Magnetism Notes, Textbook Exercise Important Questions and Answers.

Class 8 Science Chapter 4 Current Electricity and Magnetism Question Answer Maharashtra Board

Class 8 Science Chapter 4 Current Electricity and Magnetism Textbook Questions and Answers

1. Write proper words from the following group of words in the blanks and rewrite the completed sentences:
(magnetism, 4.5V, 3.0V, gravitational attraction, potential difference, potential, higher, lower, 0V)

Question a.
Water in the waterfall flows from a higher level to the lower level because of …………… .
Answer:
Water in the waterfall flows from a higher level to the lower level because of gravitational attraction.

Question b.
In an electric circuit, electrons flow from a point of potential to the point of ……….. potential.
Answer:
In an electric circuit, electrons flow from a point of lower potential to the point of higher potential.

Question c.
The difference between the electrostatic potential of the positive end and the negative end of an electric cell is the …………. of the cell.
Answer:
The difference between the electrostatic potential of the positive end and the negative end of an electric cell is the potential difference of the cell.

Question d.
Three electric cells of potential difference 1.5 V each have been connected as a battery. The potential difference of the battery will be ……………… V.
Answer:
Three electric cells of potential difference 1.5 V each have been connected as a battery. The potential difference of the battery will be 4.5 V.

Question e.
An electric current flowing in a wire creates ………………… around the wire.
Answer:
An electric current flowing in a wire creates magnetism around the wire.

2. A battery is to be formed by joining 3 dry cells with connecting wires. Show how you will connect the wires by drawing a diagram.

Question a.
A battery is to be formed by joining 3 dry cells with connecting wires. Show how you will connect the wires by drawing a diagram.
Answer:

3. In an electric circuit, a battery and a bulb have been connected and the battery consists of two cells of equal potential difference. If the bulb is not glowing, then which tests will you perform in order to find out the reason for the bulb not glowing?

Question a.
In an electric circuit, a battery and a bulb have been connected and the battery consists of two cells of equal potential difference. If the bulb is not glowing, then which tests will you perform in order to find out the reason for the bulb not glowing?
Answer:
If you can see the filament of the bulb, check whether it is intact or broken. Check whether the cells are connected in a proper manner:

Or in a wrong way:
If they are connected in a wrong way as shown above, the total potential difference will be 2V + (-2V) = zero.
Figures for reference:

4. Electric cells having potential difference 2V each have been connected in the form of a battery. What will be the total potential difference of the battery in both cases?

Question a.
Electric cells having potential difference 2V each have been connected in the form of a battery. What will be the total potential difference of the battery in both cases?

Answer:
(i) 6V
(ii) 8V.
[Note: In (i), three cells are connected in series.
∴ Total potential difference = 2V + 2V + 2V = 6V.
In (ii), four cells are connected in series.
∴ Total potential difference = 2V + 2V + 2V + 2V
= 8 V]

5. Describe the construction, working and usefulness of a dry cell, with the help of a diagram.
Question a.
Describe the construction, working and usefulness of a dry cell, with the help of a diagram.
Answer:

Dry cell:
Take a lead dry cell and remove its outer coating. Inside you will find a whitish, metal layer. This is the zinc (Zn) metal layer. This is the negative terminal of the cell. Now, carefully break open this layer. There is another layer inside. An electrolyte is filled between these two layers.

The electrolyte contains negatively charged and positively charged ions. These are the carriers of electricity. The electrolyte is a wet pulp of zinc chloride (ZnCl₂) and ammonium chloride (NH₄Cl). There is a graphite rod at the centre of the cell. This is positive terminal of the cell. A paste of manganese dioxide (MnO₂) is filled outside the rod. Because of the chemical reactions of all these chemicals, electrical charge is produced on the two terminals (graphite rod and zinc layer) and an electric current flows in the circuit.

Due to the wet pulp used in this cell, the chemical reaction proceeds very slowly. Hence a large electric current cannot be obtained from this. Compared to the electric cells using liquids, the shelf life of dry cells is longer. Dry cells are very convenient to use as these can be held in any direction with respect to ground and can be used in mobile instruments such as radio sets, wall clocks and torches.

6. Describe the construction and working of an electric bell with the help of a diagram.

Question a.
Describe the construction and working of an electric bell with the help of a diagram.
Answer:
Figure shows the construction of an electric bell and also the electric circuit. The bell consists of an electromagnet, contact screw, iron strip, metal striker and metal gong. A coil of copper wire wound around an iron piece works as an electromagnet and an iron strip along with a striker is fitted near it. A contact screw touches the strip.

The circuit is closed with the key. The current flows in the circuit when the screw is in contact with the iron strip. The current – carrying coil becomes a magnet and attracts the iron strip towards it. As a result, the metal striker hits the metal gong producing sound. At the same time, the screw loses the contact with the strip. The circuit is now incomplete.

Hence, no current flows in the circuit. Therefore, the electromagnet loses its magnetism and the electric iron strip returns to its initial condition, making contact with the screw. As the circuit is now completed, the electromagnet attracts the iron strip and the striker strikes the gong producing sound.

The action repeats itself and the bell continues to ring till the circuit is broken by opening the key in the circuit.
The working of the electric bell is thus based on the magnetic effect of electric current.

Project:

Present all the activities that you performed in this chapter in Science exhibition.

Class 8 Science Chapter 4 Current Electricity and Magnetism Additional Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
The SI unit of electric charge is the ……………… .
Answer:
The SI unit of electric charge is the coulomb.

Question 2.
The SI unit of electric current is the ……………… .
Answer:
The SI unit of electric current is the ampere.

Question 3.
The SI unit of electric potential is the ………………. .
Answer:
The SI unit of electric potential is the volt.

Question 4.
1 ampere = 1 coulomb per …………… .
Answer:
1 ampere = 1 coulomb per second.

Question 5.
When a glass rod is rubbed on a silk cloth, the glass rod acquires …………… charge.
Answer:
When a glass rod is rubbed on a silk cloth, the glass rod acquires positive charge.

Rewrite the following statements selecting the correct options:

Question 1.
The potential difference between the two electrodes of the lead-acid cell is nearly ………………. .
(a) 1 V
(b) 1.2 V
(c) 1.5 V
(d) 2 V
Answer:
(d) 2 V

Question 2.
The Ni-Cd cell delivers a potential difference of …………….. .
(a) 1 V
(b) 1.2 V
(c) 1.5 V
(d) 2 V
Answer:
(b) 1.2 V

Question 3.
…………….. is a scalar quantity.
(a) Force
(b) Acceleration
(c) Velocity
(d) Electric current
Answer:
(d) Electric current

Question 4.
The working of an electric bell is based on ………….. .
(a) the heating effect of electric current
(b) the chemical effect of electric current
(c) the magnetic effect of electric current
(d) the optical effect of electric current
Answer:
(c) the magnetic effect of electric current

Question 5.
The coulomb is the SI unit of electric ………….. .
(a) current
(b) resistance
(c) potential
(d) charge
Answer:
(d) charge

State whether the following statements are True or False:

Question 1.
The SI unit of electric potential is the ampere.
Answer:
False. (The SI unit of electric potential is the volt. OR The SI unit of electric current is the ampere.)

Question 2.
In the external circuit, the conventional current flows from the positive terminal of the cell to the negative terminal of the cell.
Answer:
True.

Question 3.
Very small current flows when lightning occurs.
Answer:
False. (A large current flows when lightning occurs.)

Question 4.
Sensation is felt by us due to a microscopically small current flowing to the brain.
Answer:
True.

Question 5.
In a car battery, a current is produced by the flow of both negatively and positively charged particles.
Answer:
True.

Identify the odd term:

Question 1.
Pressure exerted by a liquid, Electric current, Electric potential difference, Buoyant force.
Answer:
Buoyant force. It is a vector quantity. Others are scalar quantities.

Question 2.
Electric bulb, Electric heater, Electric bell, Electric iron.
Answer:
Electric bell. Its working is based on the magnetic effect of electric current. The working of other devices is based on the heating effect of electric current.

Answer the following questions in one sentence:

Question 1.
State the relation among the SI units of electric current, electric charge and time.
Answer:
1 ampere = 1 coulomb per second.

Question 2.
Name the positive terminal of the dry cell.
Answer:
The graphite rod at the centre is the positive terminal of the dry cell.

Question 3.
What constitutes an electric current in a metal?
Answer:
A continuous flow of electrons constitutes an electric current in a metal.

Question 4.
What is a battery?
Answer:
A group of two or more cells connected in series to obtain more potential difference is called a battery.

Question 5.
What is a solar cell?
Answer:
A solar cell is a device that converts solar energy into electrical energy.

Question 6.
State one characteristic of the Ni-Cd cell.
Answer:
The Ni-Cd cell is rechargeable.

Question 7.
Give one example in which the magnetic effect of electric current is used.
Answer:
The working of an electric bell is based on the magnetic effect of electric current.

Answer the following questions:

Question 1.
When do we get current electricity?
Answer:
We get current electricity when charged particles such as electrons, positive ions and negative ions are made to flow in a conductor by applying electric force.

Question 2.
Explain the concept of electrostatic potential (electric potential).
Answer:
A liquid flows from a higher level to a lower level. Heat flows from a body at a higher temperature to a body at a lower temperature. Also when different parts of a body are at different temperatures, heat flows from the part at a higher temperature to the part at a lower temperature.

Similarly, a positive charge (free to move) flows from a point at a higher electric level to a point at a lower electric level and a negative charge (free to move) flows from a point at a lower electric level to a point at a higher electric level. The electric level deciding the direction of flow of electric charge is called electrostatic potential (electric potential).

Question 3.
What is the SI unit of electric potential?
Answer:
The SI unit of electric potential is the volt (V).
[Note : This unit is named in honour of Alessandro Volta (1745-1827), Italian physicist, the inventor of the electric battery.]

Question 4.
What is potential difference?
Answer:
Potential difference is the difference
between the potentials at two points. It is similar to the height of a waterfall or the temperature difference between a hot body and a cold body. Potential difference is expressed in volt.

Try this: 

Take connecting copper wires and connect the ‘circuit’ as shown in Fig.(a). No current is seen to flow in the bulb. Now connect in the same ‘circuit’ a 1.5 V dry cell available in the market as shown in Fig.(b). Now it will be realized from glowing of the bulb that a current is flowing in the circuit. Electrons in the wire flow due to the potential difference between the two ends

In Fig.(a), there is no current as ) there is no potential difference in the absence of any cell. Current starts flowing in the circuit as soon as the potential difference is applied. The unit of potential difference in SI system is the volt (V). We will learn about it in the next standard.

Question 5.
What is electric circuit or electrical circuit?
Answer:
A continuous path consisting of conducting wires, a switch or a plug key and other resistances (for example, resistance of an electric bulb) between the terminals of a cell (or a battery) along which an electric current flows is called an electric circuit.

Question 6.
What is electric current?
Answer:
Electric current is the electric charge flowing through a conductor, such as a metal wire, per unit time.

Question 7.
What is one ampere?
Answer:
If one coulomb of charge is passing through any cross section of a conductor in one second, the amount of current flowing through it is called one ampere.
[Note: 1 ampere = 1 coulomb per second OR 1A = 1 C/s. The coulomb is named in honour of Charles Augustin de Coulomb (1736 – 1806), French physicist. The ampere is named in honour of Andre Ampere (1175 – 1836), French physicist and mathematician.]

Think about it:

Question a.
How can we measure water flow emerging from a pipe? We can find it from the amount of water (litres) coming out in a specific time period. How then is the electric current measured?
Answer:
Electric current, I = Q/t. In principle, if we can measure the quantity of charge (Q) flowing through a cross section of a conductor in time t, we can determine the current (i) using this formula (for a steady current). In practice, this is not done. Usually, electric current is measured using the magnetic effect of electric current. One can also use the heating effect and chemical effect of electric current for measurement of electric current.

Question 8.
What is an electric cell? What is its main function?
Answer:
An electric cell is a general device used to produce a uniform flow of charges in a circuit. Its main function is to maintain a constant potential difference between its two terminals.

Question 9.
Name ten devices in which electric cells are used.
Answer:
Electric cells are used in radio sets, wall clocks, wrist watches, torches, toys, mobile phones, cars, invertors, remote controls, ships, submarines, satellites, etc.

Question 10.
Draw a neat labelled diagram to show the design of the lead-acid cell and explain its principle of working.
Answer:
The lead-acid cell contains two electrodes, Pb and PbO₂, dipped in dilute H₂SO₄. Chemical reaction between the substances in the cell produces electric charges on the electrodes. PbO₂ carries a positive charge and Pb carries a negative charge. The potential difference between the electrodes is nearly 2V.

If a load, such as a bulb, is connected externally between the two electrodes, an electric current flows through it. It can deliver a large current. This cell can be recharged after getting electrically discharged.

Question 11.
State applications of the lead-acid cell.
Answer:
Lead-acid cells are connected in series to obtain higher potential difference. The lead-acid battery is used in cars, trucks, motorcycles and uninterrupted power supplies (UPS).

Question 12.
What is the potential difference delivered by the Ni-Cd cell?
Answer:
The potential difference delivered by the Ni-Cd cell is (about) 1.2 V.
[Note: In this cell, nickel oxide is the positive electrode and cadmium is the negative electrode. It is often used as a dry cell and it can be recharged. These cells are used in some portable machines that run on electricity like a drilling machine or a gardening tool.]

Question 13.
Draw a neat labelled diagram of a simple electric circuit containing a cell, an electric bulb and a plug key. What happens when the key is (i) open (ii) closed?
Answer:

(i) When the key is open, there is no current in the circuit. Hence, the bulb does not glow.
(ii) When the key is closed, a current flows in the circuit. Hence, the bulb glows.

Figure for reference:
Here, six cells can be connected in series to obtain more potential difference.

Research:
Lithium ion cells are used in modern equipment for example, a smart phone, laptop, etc. These cells can be recharged. More electrical energy can be stored in these cells as compared to that in Ni-Cd cells.

Question 14.
See Fig. What is the potential difference between A and B if each cell delivers a potential difference of 2V?

Answer:
Potential difference between A and B
= 2V + 2V + (-2V) + 2V = 4V.

Use your brain power!

Question a.
You must have seen the car battery available in the market. It is called a battery and not a cell. Why?
Answer:
In a car battery, a number of cells are connected in series to obtain more potential difference.

Here, two identical cells are connected in parallel. The potential difference between A and B is 2V. This arrangement can be used for a longer time compared to a single cell.

Series and parallel arrangement for higher potential difference and longer life.
Here, the potential difference between A and B is 8V.

Try this:

Magnetic effects of electric current :
Activity 1 :
Take the inside tray of a used up matchbox. Place a small magnetic needle inside the tray. Now take a long connecting wire and wind it around the tray. Complete the electric circuit by connecting in it, this wire, electric cell, plug key and a bulb Figure.

Mark the position of the magnetic needle. Take a bar magnet near to the magnetic needle.
1. What do you observe? Keep looking at the needle and close the plug key. The bulb will light up, and you will realize that the current has started flowing.
2. Does the magnetic needle change its position? Now open the plug key.
3. Does the magnetic needle come back to the original position?
4. What will you conclude from this experiment?
You know that a magnetic needle is indeed a magnet. You have seen that the magnetic needle changes its direction when a bar magnet is taken near the magnetic needle. Also, you have observed that the magnetic needle changes its direction when a current starts flowing in the circuit. This means that magnetic field is created when an electric current flows in a wire. Hans Christian Oersted made this observation first. Briefly we can say that when an electric current passes through a wire, a magnetic field is produced around that wire.
Answer:

1. The magnetic needle is deflected.
2. Yes.
3. Yes.
4. The electric current produces a magnetic field around a current-carrying conductor.

Activity 2 :
Take a metre long flexible copper wire having resistive coating and wind it tightly on a long iron screw. Connect the two ends of the wire in a circuit as shown in the Figure. Also connect an electric cell and a plug key in the circuit. Keep 2-4 iron pins/small nails near the screw. Now start the current in the circuit by plugging the key. It will be noticed that the pins/nails have stuck to the tip of the screw. Will the pins/nails continue to stick when the plug key is opened?

Answer:
No.
When the electric current flows in the wire, magnetism is produced in the coil around the screw and because of that the screw also attains magnetism. As soon as the current is stopped, this magnetism vanishes. The system of the coil and the screw is called an electromagnet. You have seen various uses of the electromagnet in the sixth standard. Electromagnets are used to produce a strong magnetic field useful in scientific research.

Question 15.
What is an electromagnet? State ! its applications.
Answer:
If a coil is wound around an iron screw (or an iron rod) and a current is passed through the coil with a cell (or a battery), the screw behaves as a magnet as long as there is current in the coil. The i system of the coil and the screw is called an electromagnet. It is an example of magnetic effect of electric current.
Applications: Electric bell, cranes for moving heavy loads from one place to another, toys that run on electric cells.

Question 16.
How can the strength of an electromagnet be increased?
Answer:
The strength of an electromagnet can be increased by increasing the current producing the magnetic field.

Question 17.
What is the use of the elastic iron strip in the electric bell?
Answer:
Due to the elastic iron strip, the making and breaking of the circuit occur alternately and the bell continues to ring as long as the key in the circuit is closed.

Question 18.
What will happen if the elastic iron strip in the electric bell loses its flexibility?
Answer:
When the circuit breaks and the electromagnet loses its magnetism, the strip, due to loss of flexibility, will not return to its normal position of contact with the screw. Hence, the circuit will not be completed and the bell will not ring.

Balbharati Maharashtra State Board 8th Std Science Textbook Solutions 

• Living World and Classification of Microbes Class 8 Science Textbook Solutions
• Health and Diseases Class 8 Science Textbook Solutions
• Force and Pressure Class 8 Science Textbook Solutions
• Current Electricity and Magnetism Class 8 Science Textbook Solutions
• Inside the Atom Class 8 Science Textbook Solutions
• Composition of Matter Class 8 Science Textbook Solutions
• Metals and Nonmetals Class 8 Science Textbook Solutions
• Pollution Class 8 Science Textbook Solutions
• Disaster Management Class 8 Science Textbook Solutions
• Cell and Cell Organelles Class 8 Science Textbook Solutions

Std 8 Science Chapter 6 Composition of Matter Question Answer Maharashtra Board

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 6 Composition of Matter Notes, Textbook Exercise Important Questions and Answers.

Class 8 Science Chapter 6 Composition of Matter Question Answer Maharashtra Board

Class 8 Science Chapter 6 Composition of Matter Textbook Questions and Answers

1. Choose the appropriate option and rewrite the following statements:

Question a.
The intermolecular force is ……………. in the particles of solid.
(a) minimum
(b) moderate
(c) maximum
(d) indefinite
Answer:
(c) maximum

Question b.
Solids retain their volume even when external pressure is applied. This property is called …………… .
(a) plasticity
(b) incompressibility
(c) fluidity
(d) elasticity
Answer:
(d) elasticity

Question c.
Matter is classified into the types mixture, compound and element, by applying the criterion …………… .
(a) states of matter
(b) phases of matters
(c) chemical composition of matter
(d) all of these
Answer:
(c) chemical composition of matter

Question d.
Matter that contain two or more constituent substances is called ……… .
(a) mixture
(b) compound
(c) element
(d) metalloid
Answer:
(a) mixture

Question e.
Milk is an example of type of matter called …………. .
(a) solution
(b) homogeneous mixture
(c) heterogeneous mixture
(d) suspension
Answer:
(c) heterogeneous mixture

Question f.
Water, mercury and bromine are similar to each other, because the three are ……….. .
(a) liquids
(b) compounds
(c) nonmetals
(d) elements
Answer:
(a) liquids

Question g.
Valency of carbon is 4 and that of oxygen is 2. From this, we understand that there are …………. chemical bond/bonds between the carbon atom and one oxygen atom in the compound- carbon dioxide.
(a) 1
(b) 2
(c) 3
(d) 4.
Answer:
(b) 2

2. Identify the odd term out and explain.

Question a.
Gold, silver, copper, brass.
Answer:
Brass. (Others are elements.)

Question b.
Hydrogen, hydrogen peroxide, carbon dioxide, water vapour.
Answer:
Hydrogen. (Others are compounds.)

Question c.
Milk, lemon juice, carbon, steel.
Answer:
Carbon. (Others are mixtures.)

Question d.
Water, mercury, bromine, petrol.
Answer:
Petrol. (Others are inorganic compounds.)

Question e.
Sugar, salt, baking soda, blue vitriol.
Answer:
Sugar. (Others are inorganic compounds.)

Question f.
Hydrogen, sodium, potassium, carbon.
Answer:
Carbon. (Others are monovalent elements)

3. Answer the following question.

Question a.
Plants synthesize glucose in sunlight with the help of chlorophyll from carbon dioxide and water and give away oxygen. Identify the four compounds in this process and name their types.
Answer:
Photosynthesis:

Carbon dioxide, water, glucose, and Chlorophyll are compounds.
Types: Organic compounds: Glucose
Inorganic compounds: Carbon dioxide and water
Complex compounds: Chlorophyll.

Question b.
In one sample of brass, the following ingredients were found: copper (70%) and zinc (30%). Identify the solvent, solute and solution from these.
Answer:
Brass is an alloy, it contains 70% copper and 30% zinc. The largest proportion is solvent, i.e. copper. The smaller proportion is solute, i.e. zinc. The solution is Brass.

Question c.
Seawater tastes salty due to the dissolved salt. The salinity (the proportion of salts in water) of some water bodies Lonar lake – 7.9%, Pacific Ocean 3.5%, Mediterranean sea – 3.8%, 5 Dead sea – 33.7%. Explain two characteristics of mixtures from the above information.
Answer:

1. The constituents of a mixture (the proportion of salts in water) do not combine chemically.
2. Their constituents are present in any proportion by weight.
3. The constituent of a mixture can be separated by a physical process.

4. Give two examples each.

Question a.
Liquid element.
Answer:
Mercury (Hg), Bromine (Br₂)

Question b.
Gaseous element.
Answer:
Hydrogen (H₂), Oxygen (O₂).

Question c.
Solid element.
Answer:
Iron (Fe), Copper (Cu), Silver (Ag).

Question d.
Homogeneous mixture.
Answer:
Sea water, blue vitriol dissolved in water.

Question e.
Colloid.
Answer:
Milk, blood.

Question f.
Organic compound.
Answer:
Glucose, urea.

Question g.
Complex compound.
Answer:
Chlorophyll, Haemoglobin.

Question h.
Inorganic compound.
Answer:
Soda, rust, limestone.

Question i.
Metalloid.
Answer:
Silicon, arsenic.

Question j.
Element with valency 1.
Answer:
Sodium (Na), potassium (K), chlorine (Cl).

Question l.
Element with valency 2.
Answer:
Magnesium (Mg), Calcium (Ca).

5. Write the names and symbols of the constituent elements and identify their valencies from their molecular formulae given below:
KCl, HBr, MgBr₂. K₂O, NaH, CaCl₂, CCl₄, HI, H₂S, Na₂S, FeS, BaCl₂.

Question a.
Write the names and symbols of the constituent elements and identify their valencies from their molecular formulae given below:
KCl, HBr, MgBr_2, K₂O, NaH, CaCl₂, CCl₄, HI, H₂S, Na₂S, FeS, BaCl₂.
Answer:

6. Chemical composition of some matter is given in the following table. Identify the main type of matter from them.

Question a.
Chemical composition of some matter is given in the following table. Identify the main type of matter from them.

Answer:

7. Write scientific reason.

Question a.
Hydrogen is combustible, oxygen helps combustion, but water helps to extinguish fire.
Answer:

1. Water is a compound of hydrogen and oxygen.
2. In a compound, the constituents do not retain their individual properties. Hence, hydrogen is combustible and oxygen helps combustion, but water is neither combustible nor supports combustion, it helps to extinguish fire.

Question b.
The constituent substances of a colloid cannot be separated by oridinary filtration.
Answer:

1. A colloidal solution is heterogeneous.
2. The diameters of colloidal particles are of the order of 10^-5 m.
3. The particles of a colloid can easily pass through a filter paper as the pore size of a filter paper is big. Hence, the constituents of a colloidal cannot be separated by filtration.

Question c.
Lemon sherbat has sweet, sour and salty taste and it can be poured in a glass.
Answer:

1. Lemon sherbat is a mixture. It is made up of lemon juice, sugar, salt and water.
2. Formation of lemon sherbat does not involve any chemical reaction.
3. The constituents of sherbat retain their individual properties. Hence, lemon sherbat is sweet, sour and salty to taste and it can be poured in a glass.

Question d.
A solid matter has the properties of definite shape and volume.
Answer:

1. The forces among the constituent particles (atom/molecules) are called intermolecular forces.
2. In solids these forces are strong enough to keep the particles together in fixed positions, as a result solids have a definite shape and volume.

8. Deduce the molecular formulae of the compound obtained from the following pairs of elements by the cross multiplication method.

Question a.
C (Valency 4) & Cl (Valency 1)
Answer:
Step 1: Write the symbols of the constituent elements.

Step 2: Write the valency below the respective elements.

Step 3: Cross multiply the valencies.

The molecular formula: CCl₄

Question b.
N (Valency 3) & H (Valency 1)
Use your brain power!
Answer:
Step 1: Write the symbols of the constituent elements.

Step 2: Write the valency below the respective elements.

Step 3: Cross multiply the valencies.

The molecular formula: NH₃

Question c.
C (Valency 4) & O (Valency 2)
Answer:
Step 1: Write the symbols of the constituent elements.

Step 2: Write the valency below the respective elements.

Step 3: Cross multiply the valencies.

The formula: C₂O₄
The number of constituent atoms in the final molecular formula should be the smallest possible whole number. Divide the formula C₂O₄ by suitable number.
Final molecular formula obtained by dividing by ‘2’.
Molecular formula: CO₂

Question d.
Ca (Valency 2) & O (Valency 2)
Answer:
Step 1: Write the symbols of the constituent elements.

Step 2: Write the valency below the respective elements.

Step 3: Cross multiply the valencies.

The formula: Ca₂O₂
Divide the formula by suitable number ‘2’.
The molecular formula: CaO.

Project:

Question a.
Collect the wrappers of ready-made foodstuff. Use the information given and prepare a chart of foodstuff and the ingredients in it. Procure the ingredients available. Discuss with friends and teacher, test the procured ingredients with combustion test under the supervision of your teacher. Thereby identify the ingredients as organic or inorganic.

Class 8 Science Chapter 6 Composition of Matter Additional Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
………….. have no definite shape, but have a definite volume.
Answer:
Liquids have no definite shape, but have a definite volume.

Question 2.
………… have neither a definite shape nor a definite volume.
Answer:
Gases have neither a definite shape nor a definite volume.

Question 3.
The properties of a …………… are different than those of the constitute elements.
Answer:
The properties of a compound are different than those of the constitute elements.

Question 4.
The part of matter having uniform composition is called ………………. .
Answer:
The part of matter having uniform composition is called phase.

Question 5.
The heterogeneous mixture of a liquid and a solid is called a ……………. .
Answer:
The heterogeneous mixture of a liquid and a solid is called a suspension.

Question 6.
A colloid is a ………………. .
Answer:
A colloid is a heterogeneous mixture.

Question 7.
Bronze contains atoms of the elements ……………. and ………….. .
Answer:
Bronze contains atoms of the elements copper and tin.

Question 8.
When all the components of a mixture form one phase, it is called ………….. .
Answer:
When all the components of a mixture form one phase, it is called homogeneous mixture.

Question 9.
…………… is a mixture of water, lactose, fats and proteins.
Answer:
Milk is a mixture of water, lactose, fats and proteins.

Question 10.
The intermolecular force is …………….. in the gaseous state.
Answer:
The intermolecular force is very weak in the gaseous state.

Choose the appropriate option and rewrite the following statements:

Question 1.
When a liquid is poured from one container to another, its shape may change, but its volume ………….. .
(a) increases
(b) decreases
(c) remains the same
(d) none of them
Answer:
(c) remains the same

Question 2.
The property by which some solids maintain their shape even when subjected to external forces is called ………. .
(a) elasticity
(b) fluidity
(c) rigidity
(d) plasticity
Answer:
(c) rigidity

Question 3.
…………… is a complex compound.
(a) Glucose
(b) Blue vitriol
(c) Chlorophyll
(d) Soda
Answer:
(c) Chlorophyll

Question 4.
………….. is a homogeneous mixture.
(a) Sand + water
(b) Flour + water
(c) Salt + water
(d) Oil + water
Answer:
(c) Salt + water

State whether the following statements are True or False:

Question 1.
Liquids do not have a definite shape
Answer:
True.

Question 2.
Gases have a definite shape and volume.
Answer:
False. (Gases do not have shape and volume.)

Question 3.
The crystals of blue vitriol form a single phase.
Answer:
True.

Question 4.
Water is a mixture.
Answer:
False. (Water is a compound)

Question 5.
Milk is a colloid.
Answer:
True.

Question 6.
A suspension does not scatters light.
Answer:
True.

Question 7.
Copper sulphate is a mixture.
Answer:
False. (Copper sulphate is a compound.)

Question 8.
An atom forms as many chemical bonds with other atom as its valency.
Answer:
True.

Question 9.
The strength of intermolecular forces is weak in the liquid state.
Answer:
False. (The strength of intermolecular forces is moderate in the liquid state.)

Question 10.
All the gases present together constitute a single phase.
Answer:
True.

Match the column:

Question 1.

Answer:

Question 2.

Answer:

Question 3.

Answer:

Answer the following questions in one sentence:

Question 1.
Why does a solid have definite volume ?
Answer:
In solids intermolecular forces are strong enough to keep the particles together in fixed positions, as a result solids have definite volume.

Question 2.
Why does a liquid have indefinite shape?
Answer:
In a liquid intermolecular forces are not strong enough to keep the particles together in fixed positions, as a result liquid has indefinite shape.

Question 3.
Why does a gas have indefinite volume and shape?
Answer:
In a gas intermolecular forces are very weak and the distance between the particles is very large, as a result gas has indefinite volume and shape.

Question 4.
What can you say about the distance between the neighbouring particles of solid?
Answer:
The particles of solid are very close to each other and the distance between them is minimum.

Question 5.
What can you say about the distance between the constituent particles of gas?
Answer:
The intermolecular force is very weak in gases. The distance between the particles of gas is very large. They move freely and occupy all the available space.

Question 6.
State whether the mixture of oil in water is a homogeneous or heterogeneous mixture.
Answer:
The mixture of oil in water is a heterogeneous mixture.

Question 7.
State whether seawater is a homogeneous or heterogeneous mixture.
Answer:
Seawater is a homogeneous mixture.

Question 8.
Give two examples of liquid in liquid.
Answer:
Examples of liquid in liquid:
Vinegar, dilute sulphuric acid.

Question 9.
Give two examples of gas in gas.
Answer:
Examples of gas in gas: Air, cooking gas.

Question 10.
Give two examples of solid in solid.
Answer:
Examples of solid in solid: Brass, stainless steel.

Question 11.
Give two examples of gas in liquid.
Answer:
Examples of gas in liquid: Chlorinated water, hydrochloric acid.

Question 12.
Give molecular formulae of 1. potassium chloride, 2. sodium sulphide.
Answer:

1. Molecular formula of potassium chloride: KCl
2. Molecular formula of sodium sulphide: Na₂S.

Question 13.
State the molecular formula and number of hydrogen atoms in methane.
Answer:
Molecular formula of methane: CH₄
The number of hydrogen atoms in methane is 4.

Question 14.
Identify the valency of chlorine in
(i) KCl and (ii) CaCl₂.
Answer:
i. The valency of chlorine in KCl is 1.
ii. The valency of chlorine in CaCl₂ is 1.

Answer the following questions:

Question 1.
State two principal ways of classifying matter.
Answer:
Two principal ways of classifying matter are:

1. On the basis of physical state as a solid, liquid or gas.
2. On the basis of chemical constitution as an element, compound or mixture.

Question 2.
What are the different states of matter?
Answer:
The different states of matter are solid, liquid and gas.

Question 3.
Define solid.
Answer:
A substance which has a definite shape and volume is called a solid.

Question 4.
State any three characteristics of solids.
Answer:

1. Solids have a definite shape and volume.
2. Most of the solids are rigid while some are plastic and some elastic.
3. Solids have practically negligible compressibility, i.e., their volume is not very much changed by external forces.

Question 5.
What is meant by rigidity of solids?
Answer:
The property by which solids maintain their shapes when subjected to external forces is called rigidity.

Question 6.
What is meant by elasticity of solids?
Answer:
Some solids undergo a change in their shapes and volume when subjected to external forces and regain their original shapes and volume on removal of the forces. This property of solids is called elasticity.

Question 7.
What is meant by plasticity?
Answer:
Some solids are deformed by external forces and do not regain their original shapes on removal of the forces. This property of solids is called plasticity.

Question 8.
Solids have a high density and negligible compressibility. Explain.
Answer:

1. The forces among the constituent particles (atoms/molecules) are called intermolecular forces.
2. In solids these forces are strong enough to keep the particles together in fixed positions, as a result solids have a high density and negligible compressibility.

Question 9.
Define liquid.
Answer:
A substance which does not have a definite shape, but has a definite volume is called a liquid.

Question 10.
State any three characteristics of liquids.
Answer:

1. Liquids have a definite volume.
2. Liquids do not have a definite shape. They take the shape of the container in which they are stored.
3. When they spill on a plane surface, they spread and flow in the surrounding areas, i.e., they have fluidity.
4. They have very small compressibility.

Question 11.
What is meant by fluidity?
Answer:
Liquids flow easily and change their shapes in response to external forces. This property of liquids is called fluidity. It is exhibited by gases also.

Question 12.
Liquids have fluidity and they do not have a definite shape. Explain.
Answer:
1. The forces among the constituent particles (atoms/molecules) are called intermolecular forces.
2. In liquids, the intermolecular forces are strong enough to keep the particles within the bulk in aggregation, but not strong enough to keep them in fixed positions. As a result, they flow easily and change shapes according to that of container.

Question 13.
Define gas.
Answer:
A substance which has neither a definite shape nor a definite volume is called a gas.

Question 14.
State any three characteristics of gases.
Answer:

1. Gases have neither a definite shape nor a definite volume.
2. They spread in all directions.
3. They can be compressed or expanded easily.
4. In gases intermolecular forces are very weak.

Question 15.
Gases have neither a definite shape nor a definite volume. Explain.
Answer:

1. The forces among the constituent particles (atoms/molecules) are called intermolecular forces.
2. In gases the intermolecular forces are extremely weak. As a result, the molecules of a gas move freely and a gas occupies all the available space.

Question 16.
Why are gases more compressible, than liquids?
Answer:
In liquids the distances between the neighbouring molecules are less than those in the gases. The intermolecular forces are extremely weak in gases, but not so weak in liquids. Hence, gases are more compressible than liquids.

Question 17.
What is an element? Give two examples.
Answer:
A type of matter composed of only one kind of substances where each smallest indivisible part of it has the same properties is called an element. It cannot be subdivided into simpler substances by any physical or chemical means.
Examples: Oxygen, nitrogen, silver.

Question 18.
Write any two characteristics of an element.
Answer:

1. All the atoms/molecules of an element are alike.
2. Atoms/molecules of different elements are different.
3. An element cannot be decomposed into simple substances by any chemical reaction or simple physical process.

Question 19.
What is a compound? Give two examples.
Answer:
A substance produced by a chemical reaction of two or more elements combined in a fixed proportion is called a compound.
Examples: Water, common salt, sugar.

Question 20.
Write any two characteristics of a compound.
Answer:

1. The proportion of constituent elements in a compound is constant.
2. The properties of a compound is different than those of the constituent elements.

Question 21.
What is a mixture? Give two examples.
Answer:
When two or more elements or compounds which do not react chemically with each other are mixed in any proportion, a mixture is formed.
Examples: Air, steel, milk.

Question 22.
Write any two characteristics of a mixture.
Answer:

1. The constituent molecules of mixture are different from each other and notoined by chemical bonds.
2. The proportion of constituent substances are retained in the mixture.
3. The constituents of a mixture can be separated by a physical process.

Question 23.
Classify the following into elements, compounds and mixtures:
Sugar, sodium, nitrogen, sodium carbonate, air, sulphuric acid, mercury, stainless steel, cement, potassium dichromate.
Answer:

• Elements: Sodium, nitrogen, mercury.
• Compounds: Sugar, sodium carbonate, sulphuric acid, potassium dichromate.
• Mixtures: Air, stainless steel, cement.

Question 24.
Write the composition of the following materials by means of chemical formulae and classify them accordingly.

Answer:

Question 25.
What is meant by an organic compound? Give two examples.
Answer:
The compound which when heated strongly gives black coloured carbon residue is called an organic compound or carbon compound.
Examples: Carbohydrates, proteins, hydrocarbons (petrol, cooking gas).

Question 26.
What is meant by an inorganic compound? Give two examples.
Answer:
Compounds which when heated strongly decomposes to give a residue behind are called inorganic compounds.
Examples: Common salt, rust, blue vitriol, limestone.

Question 27.
What is meant by complex compounds? Give two examples.
Answer:
The molecules of compounds which have a complex structure formed by many atoms and in the centre of this structure metal atoms are also included are called complex compounds.
Examples: Haemoglobin, chlorophyll.

Question 28.
Classify the following compounds into organic compounds, inorganic compounds and complex compounds.
Petrol, common salt, haemoglobin, blue vitriol, cyanocobalamine, cooking gas.
Answer:

• Organic compounds: Petrol, cooking gas
• Inorganic compounds: Common salt, blue vitriol.
• Complex compounds: Cyano cobalamine, haemoglobin.

Question 29.
What is a phase?
Answer:
The part of matter with uniform composition is called a phase.

Question 29.
What is a homogeneous mixture? Give two examples.
Answer:
When all the components of a mixture form one phase, it is called homogeneous mixture.
Example: Solution of blue vitriol in water, solution of sugar in water.

Question 30.
What is heterogeneous mixture? Give two examples.
Answer:
When the components of a mixture are distributed into two or more phases, it is called a heterogeneous mixture.
Examples: Oil and water, sand and water.

Question 31.
Define solution or What is meant by a solution? Give two examples.
Answer:
A homogeneous mixture of two or more substances is called a solution.
Examples: Seawater, sugar, syrup.

Question 32.
What is meant by a solvent?
OR
Define solvent. Give two examples.
Answer:
The component which is present in largest proportion in a solution is called a solvent.
Examples:

1. In sea water, water is the solvent.
2. In tincture iodine, alcohol is the solvent.

Question 33.
What is meant by a solute?
OR
Define solute. Give two examples.
Answer:
The component of a solution which is present in smaller proportion than the solvent is called a solute.
Examples:

1. In sea water, salt is a solute.
2. When a small of amount of sugar is dissolved in water, sugar is the solute in the solution.

Question 34.
Define suspension.
OR
What is meant by a suspension?
Answer:
A heterogeneous mixture of a liquid and a solid is called a suspension. The diameter of the solid particles in a suspension is larger than 10^-4 m.

Question 35.
Define colloid.
Answer:
A heterogeneous mixture in which the particles cannot be seen with a naked eye is called a colloid. The diameter of colloidal particles is around 10^-5 m.

Question 36.
State the characteristics of a solution.
Answer:

1. A solution is clear and transparent, it passes through a filter paper.
2. The particles are not visible to the naked eye.
3. A light can easily pass through it without scattering.
4. A solution is homogeneous mixture.

Question 37.
State the characteristics of a suspension.
Answer:

1. In suspension, the solute particles do not dissolve but remain suspended in it. The liquid and solid components of suspension are separated by filtration.
2. The particles are visible to the naked eye.
3. The particles in suspension are of very small size and scatter a beam of light passing through it.
4. It is heterogeneous in nature.

Question 38.
State the characteristics of a colloid.
Answer:

1. In a colloid, the particles are spread uniformly throughout the solution.
2. The size of the particles is less than that of the particles in a suspension.
3. The particles are not visible to the naked eye.
4. The particles scatter a beam of light.
5. A colloidal solution appears to be homogeneous, but actually it is heterogeneous. ‘

Question 39.
Give two examples of each of the following:

1. Phase
2. Homogeneous matter
3. Heterogeneous matter
4. Homogeneous mixture
5. Heterogeneous mixture
6. Solution
7. Suspension
8. Colloid.

Answer:

1. Phase: (i) Solid: Sodium chloride, blue vitriol, sand, (ii) Liquid: Water, alcohol, (iii) Gas: Chlorine, ammonia.
2. Homogeneous matter: Blue vitriol (solid), a solution of blue vitriol in water (a solid in a liquid), chlorinated water (a gas in a liquid).
3. Heterogeneous matter: Sand and water, sand and alcohol, blue vitriol and sand.
4. Homogeneous mixture: A solution of sodium chloride in water, air, a mixture of water and alcohol.
5. Heterogeneous mixture: A mixture of sand and blue vitriol, sodium chloride and iron filings, oil and water.
6. Solution: Seawater, a solution of sugar in water, a solution of blue vitriol in water.
7. Suspension: A mixture of sand and water, sand and alcohol, muddy water, limestone in water.
8. Colloid: Milk, milk of magnesia, blood, printing ink.

Question 40.
State the different types of solutions. Give one example.
Answer:
The different types of solutions:

• Liquid in liquid. Examples: Vinegar, dilute sulphuric acid.
• Gas in gas. Example: Air.
• Solid in solid. Examples: Brass, stainless steel, bronze.
• Gas in liquid. Examples: Chlorinated water.

Question 41.
Classify the following into homogeneous solution and heterogeneous solution?
Soda water, potassium permanganate solution, milk, alcohol in water, ink solution, wheat flour in water.
Answer:

• Homogeneous solution: Soda water, potassium permanganate solution, alcohol in water.
• Heterogeneous solution: Milk, ink solution, wheat flour in water.

Question 42.
Classify the following into solution, suspension and colloids:
Milk, sand in water, lemonade, smoke, oxygen in water.
Answer:

• Solution: Lemonade, oxygen in water.
• Suspension: Sand in water.
• Colloids: Milk, smoke.

Question 43.
What is meant by molecular formula?
Answer:
The number of atom of each of the constituent elements present in one molecule of a compound is called molecular formula.

Question 44.
What is meant by valency of an element?
Answer:
The capacity of an element to combine with another element is known as valency.

Question 45.
Deduce the molecular formulae of the compound obtained from the following pairs of elements by the cross multiplication method.
Answer:
Question a.
H (Valency 1) and O (Valency 2)
Answer:
Step 1: Write the symbols of the constituent elements.

Step 2: Write the valency below the respective elements.

Step 3: Cross multiply the valencies.

∴ The molecular formula: H₂O.

Question b.
Fe (Valency 2) and S (Valency 2)
Answer:
Step 1: Write the symbols of the constituent elements.

Step 2: Write the valency below the respective elements.

Step 3: Cross multiply the valencies.

The molecular formula: FeS

Question c.
The valencies of the atom H, O and N are 1, 2 and 3 respectively. The molecular formulae of these gaseous elements are H₂, O₂ and N₂ respectively. How many chemical bonds are there in each of these molecules?
Answer:
Chemical bond in H₂ is one

Chemical bond in O₂ are two

Chemical bond in N₂ are three

Give scientific reasons:

Question 1.
Hydrogen is an element.
Answer:

1. Hydrogen has only one kind of atoms.
2. Hydrogen cannot be further divided into new substances by any physical or chemical means. Therefore, hydrogen is an element.

Question 2.
Water is a compound.
Answer:

1. The composition of water is same throughout i.e., the elements hydrogen and oxygen whose atoms are combined in the ratio by weight is always 1 : 8.
2. The properties of water are totally different from those of its constituents, i.e. hydrogen and I oxygen. Hence, water is a compound.?

Question 3.
Air is a mixture.
Answer:

1. Air contains nitrogen, oxygen and other gases.
2. These gases retain their original properties. They do not combine with each other. Hence, air is a mixture.

Question 4.
A potassium permanganate solution in water is a homogeneous mixture, while a mixture of oil and water is a heterogeneous mixture.
Answer:

1. In a potassium permanganate solution in water the constituents, i.e. potassium permanganate and water are uniformly mixed throughout.
2. The properties and composition of a homogeneous mixture are the same throughout the mixture. Hence, potassium permanganate solution is a homogeneous mixture.
3. In a mixture of oil and water, the constituents are not uniformly mixed throughout the mixture.
4. The properties and composition of a heterogeneous mixture are not the same throughout the mixture. Hence, a mixture of oil and water is a heterogeneous mixture.

Question 5.
Milk is a colloid.
Answer:

1. In milk, the particles are spread uniformly throughout and due to very small size of the particles, milk appears to be homogeneous.
2. But milk is a colloid solution and it is a heterogeneous mixture. Here, milk is liquid particles of proteins and fats having a diameter around 10^-5 m dispersed in the aqueous medium. Hence, a milk is a colloid.

Distinguish between the following:

Question 1.
Answer:

Question 2.
Liquids and Gases:
Answer:

Question 3.
Solids and Gases:
Answer:

Question 4.
Element and Compound:
Answer:

Question 5.
Compound and mixture:
Answer:

Question 6.
Colloidals and Suspension:
Answer:

Activity-based questions:

Activity 1:
Apparatus: Plastic jar, balloon, thread
Material: Mustard seeds
Take some mustard seeds in a transparent plastic jar. Thread a long thread at the centre of a big balloon by means of a needle and tie it tight. Stretch this rubber diaphragm and fix it on the mouth of the jar by means or a rubber band. Pull the diaphragm up and down with the help of the thread first slowly, then with moderate force and then vigorously. Record your observation in the following table.

Question 1.

Answer:

Activity 2:
Apparatus: Hammer, sand paper
Material: Iron nail, copper wire, aluminium wire, coal.
Take the following objects: iron nail/sheet, copper wire, aluminium wire, a piece of coal. Rub each object on a fresh surface of sandpaper and observe. Hammer each object with force. (Take care not to hurt yourself.) Record your observations in the following table.
The objects in the activity are made of the elements iron (Fe), copper (Cu), aluminium (Al) and carbon (C); respectively. Fill the following table on the basis of the observations obtained on doing the above two tests on each of the objects.

Question 1.

Answer:

Activity 3:
Apparatus: Evaporating dish, tripod stand, burner, etc.
Chemicals: Camphor, washing soda, blue vitriol, sugar, glucose, urea.
Keep the evaporating dish on the tripod stand. Take some camphor in the evaporating dish. Heat the camphor in the dish strongly with the help of a burner. Find out what remains behind in the evaporating dish. Repeat the above procedure using limestone, washing soda, blue vitriol, sugar, glucose and urea instead of camphor. Record your observation in the following table. (Do this activity carefully under the supervision of your teacher, as some of the powders may catch fire.)

Question 1.

Answer:

Activity 4: (Textbook page 43)
Apparatus: Beakers, rods
Chemicals: Blue vitriol, sand, water, etc.
Take three beakers. Take a little sand and water in the first beaker. Take some crystals of blue vitriol and water in the second beaker. Take some blue vitriol and sand in the third beaker. Stir the materials in all the three beakers and observe. Record your observation in the following table.

Question 1.

Answer:

Question 2.
In the above activity after stirring a homogeneous mixture is formed in only one beaker? Which is that?
Answer:
The homogeneous mixture is formed in the second beaker. It is a solution of blue vitriol.

Activity 5:
Apparatus: Beaker, conical flask, funnel, filter paper
Chemicals: Common salt, saw dust, milk.
Procedure: Take three beakers. Take 10 g common salt in the first beaker, 10 g saw dust in the second beaker and 10 ml milk in the third beaker. Add 100 ml water to all the three beakers and stir. Which of the mixtures shows separate water phase ? Place the three beakers in front of a vertically held paper and pass a laser beam through the beakers from the opposite side. (Use the laser beam under the guidance of teacher.) At the same time observe what appears on the paper in front of the beaker. Also look at the beaker from the side. Arrange three filtration assemblies using conical flask, funnel and filter paper for doing filtration. Stir the mixtures in the three beakers and carry out filtration. Record all the observations in the following table.

Question 1.

Answer:

Activity 6: (Textbook page 44)
Apparatus: Horseshoe magnet, evaporating dish, burner. Chemicals: Iron filings, sulphur.
Procedure: Take two evaporating dishes. Take 7 g iron filings in the first dish and 4 g sulphur in the second. Take a horseshoe magnet near the matter in both the dishes and observe. Transfer the entire iron filings from the first dish to the second, stir with a glass rod and observe by taking the horseshoe magnet near the matter. Also observe the colour of the matter. Now heat the matter in the second dish for a while and let it cool. Observe the colour change, if any in the matter and observe whether there is any effect of the horseshoe magnet on it. Record all the observation in the following table.

Question 1.

Answer:

Complete the following:

Question 1.
Complete the table:

Answer:
Molecular formulae of some compounds are given in the following table. Use these to fill in the gaps in the table.

Question 2.
Complete the table:

Answer:
Molecular formulae of various compounds formed by hydrogen with other elements are given in the following table. From that, deduce the valencies of the concerned elements.

Question 3.
Complete the table:

Answer:

Balbharati Maharashtra State Board 8th Std Science Textbook Solutions 

• Living World and Classification of Microbes Class 8 Science Textbook Solutions
• Health and Diseases Class 8 Science Textbook Solutions
• Force and Pressure Class 8 Science Textbook Solutions
• Current Electricity and Magnetism Class 8 Science Textbook Solutions
• Inside the Atom Class 8 Science Textbook Solutions
• Composition of Matter Class 8 Science Textbook Solutions
• Metals and Nonmetals Class 8 Science Textbook Solutions
• Pollution Class 8 Science Textbook Solutions
• Disaster Management Class 8 Science Textbook Solutions
• Cell and Cell Organelles Class 8 Science Textbook Solutions

Std 6 Science Chapter 4 Disaster Management Question Answer Maharashtra Board

Balbharti Maharashtra State Board Class 6 Science Solutions Chapter 4 Disaster Management Notes, Textbook Exercise Important Questions and Answers.

Class 6 Science Chapter 4 Disaster Management Question Answer Maharashtra Board

1. What are the emergency contact numbers of the following:

Question a.
Police Control Room
Answer:
100

Question b.
Fire brigade
Answer:
101

Question c.
Ambulance
Answer:
102

Question d.
National level single emergency number for disaster relief
Answer:
108

2. What first aid will you provide in the following situations?
a. Dog bite
b. Scratches/Bleeding
c. Bums/Scalds
d. Snakebite
e. Sunstroke

Question a.
Dog bite
Answer:
First aid is some immediate aid given to a victim or patient before medical treatment is available.

1. Wash the wound with a soap solution.
2. Cover the wound with a clean and dry cloth.
3. Get a doctor’s help.

Question b.
Scratches / Bleeding
Answer:

1. Make the person sit or lie down comfortably.
2. Clean the bleeding part of the bodywith water.
3. Keep it above the level of the heart.

Question c.
Bums/scalds
Answer:

a. Minor bums

1. The injured part should be washed with water or held underwater.
2. Give the victim water to drink.
3. Clean the wounds using a cotton swab soaked in an antiseptic solution.
4. Do not apply oily ointments.
5. Cover the wound using dry dressings.

b. Serious bums

1. Give emotional support.
2. Cover the wound with sterilised cloth.
3. Remove jewellery, shoes etc. if easily possible.
4. Do not touch or burst the blisters on the skin.
5. Do not apply oily ointments.
6. Do not try to remove the cloth if it is struck to the burnt skin.
7. If the patient is conscious give water to drink but avoid tea or coffee or other stimulating drinks. Get medical aid at once.

Question d.
Snakebite
Answer:

1. Wash the wound with water.
2. Give emotional support to the patient.
3. Tie a cloth tightly above the wound.
4. Get immediate medical help.

Question e.
Sunstroke
Answer:

1. Take the patient to a cool place or in the shade.
2. Sponge the whole body with cold water.
3. Place a cloth soaked in cold water on the neck.
4. Give plenty of water or liquids like sherbets to drink.
5. If the patient feels like vomiting make him prone i.e. on his/her abdomen with the head turned to one side.
6. Get medical help or shift the patient to a hospital.

3. Write the causes of the following:
a. Floods
b. Forest fires
c. Landslides/building collapse
d. Storms
e. Earthquakes

Question a.
Floods:
Answer:

1. 1. Floods is a frequently occurring natural disaster in all parts of the world.
   2. Due to excessive rains in the same place, a river overflows its banks causing a flood.
   3. The water drainage system in big cities falls short when there is heavy rainfall, resulting in choking of gutters and drainage lines.
   4. Water overflows on to the roads and surrounding houses.

Question b.
Forest fires:

1. Forest fire is an uncontrolled fire in a forest, pasture or grasslands due to natural or man-made causes.
2. Natural causes of forest fire can be lightning, volcanic eruptions, friction amongst branches of trees in extremely hot and dry weather.
3. Man-made causes of forest fires are clearing land by burning which sometimes goes out of control.
4. Campers and hikers sometimes leave behind a potential source of ignition like a lighted cigarette or a campfire.

Question c.
Landslides/building collapse:
Answer:

1. Landslide causes due to erosion, slope movement in the downward direction, prolonged rainfall and seepage, vibration caused by earthquakes, deforestation, river erosion.
2. Building collapses: Bad design, faulty construction, foundation failure or weak foundation, extraordinary loads, earthquakes, rampant and irregular constructions.

Question d.
Storms:
Answer:
The formation of high and low air pressure belts in the atmosphere causes changes in weather resulting in strong winds or storms.

Question e.
Earthquakes:
Answer:

1. Movements in the interior of the earth release tremendous amount of energy.
2. This causes seismic waves leading to movement of the earth’s surface like tremors, shaking, cracking up.
3. Such vibrations or quaking in the earth’s crust is known as earthquake.
4. Man-made causes like mining, construction of big dams can also lead to earthquakes.

4. Answer the following questions.

Question a.
What is meant by ‘disaster’?
Answer:
A sudden event that causes large-scale damage to life, property and social aspects of a nation or society is called a disaster.

Question b.
What are the types of disasters?
Answer:
Disasters are of two types: Natural disasters and man-made disasters.

Question c.
What is meant by disaster management’?
Answer:
Taking steps to prevent disasters, making plans to face disasters and developing the capacity for that is called disaster management.

Question d.
Which are the main components of disaster management?
Answer:
Emergency planning and implementation of disaster management work are the main components of disaster management. Community participation is close, related to disaster management.

5. Find out about the work of a ‘Sarpa-mitra’.

Question a.
Find out about the work of a ‘Sarpa-mitra’.
Answer:

1. A sarpa-mitra is a friend of snakes, a person who is trained to protect, save and safeguard snakes.
2. Whenever there is a phone call from police or citizens informing the sarpa-mitras about snake sightings, they immediately rush to the situation and rescue the snake that would have been killed at the hands of people.
3. Sarpa-mitra are well trained to handle snakes by capturing them, keeping them in baskets or bags before releasing them in the wild.
4. They are in contact with the Police Department and Forest Department for rehabilitation of snakes.
5. Sarpa-mitra are also trained to perform primary first aid to snake bite victims before they are moved to hospitals.
6. Thus, the sarpa-mitra do a commendable job of saving snakes, saving human life without any monetary gains, but for sheer love of snakes.

6. Find out what a first aid kit / box contains.

Question a.
Find out what a first aid kit / box contains.
Answer:
1. First aid kit/box is a necessity at home, workplace, travelling, schools, etc.
2. It contains a cotton roll, sterilized dressing, a pair of scissors, Dettol or Savlon, Dettol soap, adhesive plaster, tablets like Crocin, necessary medicines – painkiller, Tincture iodine, Electrolyte powder, ear/eye drops, Potassium Permanganate crystals, Bumol ointment for cramps.

7. Suggest remedial measures for dealing with natural or man-made disasters.

Question a.
Suggest remedial measures for dealing with natural or man-made disasters.
Answer:

1. Fire: Use a fire extinguisher. Call the fire brigade. Run to a safe exit.
2. Building collapse: Evacuate the building immediately, seek shelter in other safe places. Call the fire brigade or rescue team. First aid should be given to injured people.
3. Road accident: Call the ambulance immediately. Give first aid if possible.
4. Flood: Do not linger in houses or areas near river banks. Seek shelter in other safe places. Move to safer places at a greater height. Do not step into water currents or drive a vehicle into them.
5. War: Take shelter in relief camps. Provide assistance in the rescue mission.
6. Bomb explosions: Take shelter in relief camps/safe place. Immediately call the police. Be alert and do not touch the unattended objects.
7. Earthquakes: Run to a safe place. Hide below a table.and do not use elevators. Use a staircase.
8. Deluge: Take the warnings and signals from the Meteorological Department keep away from river banks and low-lying areas. Take shelter in relief camps.
9. Storm: Remain in a safe place. Unplug all electrical devices. Take instructions given to people by meteorological department do not take shelter in dilapilated structures and under trees.
10. Tsunami: Move to a safer place, stay alert.
11. Drought: Save water, take care of people and cattle.
12. Landslide: Landslide may be caused due to excessive rains or cloudbusrt in hilly areas. Do not take shelter at the foot of a hill.

Activity:

Question 1.
Compile information about measures taken for disaster management in your school.

Question 2.
Make posters, advertisements, banners about disaster management.

Question 3.
Find out the people/organisations that provide aid during a disaster. Obtain their phone numbers, addresses, etc.

Class 6 Science Chapter 4 Disaster Management Important Questions and Answers

Fill in the blanks:

Question 1.
In 1993, many people died due to the earthquake at ……………… in Latur district.
Answer:
Killari

Question 2.
Even today, people of shudder at the memory of ……………… 26 July, 2005.
Answer:
Mumbai

Question 3.
In November 2015, many people died due to flooding caused by heavy rains in ……………… .
Answer:
Tamil Nadu

Question 4.
Movements in the interior of the earth release tremendous amounts of ……………… .
Answer:
energy

Question 5.
Vibrations or ……………… in the earth’s crust is known as earthquake.
Answer:
quaking

Question 6.
Man-made causes like ……………… and construction of big dams can also lead to earthquakes.
Answer:
mining

Question 7.
A frequently occurring natural disaster in all parts of the world is ………………. .
Answer:
floods

Question 8.
Forest fires spread at a ……………… speed.
Answer:
tremendous

Question 9.
Landslides occur in hilly areas due to a ……………… .
Answer:
cloudburst

Question 10.
To get protection from fire, use ……………… .
Answer:
fire extinguisher

Match the following. 

Question 1.

Answer:

State whether the following statements are True or False. If false, correct them.

Disaster Management Class 6  Question 1.
In 1993, many people died due to the earthquake at Malin in Pune district.
Answer:
False: In 1993 many people died due to the earthquake at Killari in Latur district.

Disaster Management Class 6 Exercise Question 2.
Disaster Management Class 6 ExerciseEven today, people of Mumbai shudder at the memory of July 2007.
Answer:
False: Even today people of Mumbai shudder at the memory of July 2005.

Class 6 Science Chapter 4 Disaster Management  Question 3.
Increased risk due to high density of population in a limited area can cause disaster.
Answer:
True

4 Disaster Management Exercise Question 4.
Earthquakes cause huge loss of life and property.
Answer:
True

Question 5.
Forest fire is a controlled fire in a forest, pasture or grassland.
Answer:
False: Forest fire is an uncontrolled fire in a forest, pasture or grassland.

Question 6.
Storms cause no disruption of electric supply.
Answer:
False: Storms cause disruption of electric supply.

Question 7.
Community participation is closely related to disaster management.
Answer:
True

Question 8.
National Disaster Management Authority was established in 2008.
Answer:
False: National Disaster Management Authority was established in 2005.

Question 9.
During a disaster, keep watching movies on TV.
Answer:
False: During a disaster keep watching news bulletin on TV.

Question 10.
In case of a disaster, use the website www. imd.gov.in
Answer:
True

Answer the following in one sentence:

Question 1.
What are man-made causes of earthquakes?
Answer:
Mining, construction of big dams can lead to earthquakes.

Question 2.
What are forest fires?
Answer:
A forest fire is an uncontrolled fire in a forest, pasture or grassland due to natural or man-made causes.

Question 3.
State the website to seek government’s help during disaster.
Answer:
To seek government’s help during a disaster we can log on to xvww.imd.gov.in

Question 4.
Where should we take shelter during floods?
Answer:
We should seek shelter in safe places especially safer places at great heights.

Question 5.
What is sunstroke?
Answer:
When we work in the sun continuously for a long time, the body loses a lot of water and minerals. Hence, the person experiences sunstroke.

Question 6.
Name some poisonous snakes.
Answer:
Some poisonous snakes are cobras, kraits, vipers and sea snakes.

Question 7.
What should we do when we come across a snake?
Answer:
When we come across a snake we should contact a sarpa-mitra.

Question 8.
What is first aid?
Answer:
Immediate aid given even before medical treatment is available on facing a disaster or accident is first aid.

Answer the following questions briefly:

Question 1.
What are the effects of an earthquake?
Answer:
The effects of an earthquake are:

1. Destruction of infrastructure i.e buildings, bridges, roads, railway tracks.
2. Change in the direction of the flow of river.
3. Huge loss of life and property.

Question 2.
What are the effects of floods on people?
Answer:

1. There is a huge loss of life and property.
2. Soil erosion
3. Destruction of standing crops.
4. After-effects of floods, like spread of diseases and epidemics affecting the health of the people.

Question 3.
What are the effects of storms?
Answer:

1. Great damage in the storm affected region.
2. Tremendous losses to life and property.
3. Disruption of electric supply.
4. Disruption of transport and communication.

Question 4.
What are the effects of forest fires?
Answer:

1. Great damage to natural wealth and bio-diversity.
2. Pollution of air.

Question 5.
What preventive measures should we take to protect us from fire?
Answer:
To get protection from fire, use fire extinguishers in public places like schools, hospitals, railway stations.

Question 6.
What first aid can be provided to a person if he is bleeding?
Answer:
If a person is bleeding, first make him sit or lie down comfortably. Clean the bleeding part of the body with water and keep it above the level of the heart.

Give scientific reasons:

Question 1.
Why should a dog bite victim get an injection of the anti-rabies vaccine?
Answer:
In a dog bite, there is a risk of infection of rabies through the blood, hence anti-rabies injection is given to the patient.

Question 2.
During a disaster if possible we should take shelter in relief camps.
Answer:
Relief camps provide medicines, food packets, drinking water and first aid. Since these things help victims to restart, people should take shelter in relief camps during a disaster.

Question 3.
During disaster use battery operated radios and mobile.
Answer:
During disaster, many times there is disruption of electricity, hence battery operated mobiles and radios are convenient.

Can you tell?

Question 1.
What event do you see in these pictures?
Answer:
In this picture we see –
(a) earthquakes
(b) drought
(c) flood
(d) fire
(e) storm
(f) volcanic eruptions.

Question 2.
What would you have done in these situations?
Answer:
In these situations I would have tried to save my life. (Answer:wers may vary)

Question 3.
Have you experienced such a situation yourself?
Answer:
No. (Answer:wers may vary)

Question 4.
Why do these events occur?
Answer:
This events are disasters and some occur naturally and some are man-made.

Question 5.
According to you, what can be done to deal with such a disaster?
Answer:
To deal with such a disaster, take help of some elders or ask for help immediately. Be alert and use first-aid / get some immediate aid even before medical treatment becomes available.

Use your brainpower!

Question 1.
What disaster can occur in school or on the way to school?
Answer:
1. Disasters that can occur in school: Fire in the school building, experience tremors of earthquake, school building collapses, slab in one of the classroom collapses, getting injured while playing, getting an electric shock.
2. Disasters that can occur on way to school: You meet with an accident while crossing the road or school bus meets with an accident. Area near school gets flooded.

Classify the following disasters as man-made or natural.
(fire, earthquake, leakage of chemical gases, storms, floods, tsunami, bomb explosions, collapse of a building, war, forest fire)
Answer:

Can you tell?

Question 1.
How many children are there in your class at present?
Answer:
There are 50 children in my class at present. (Answers may vary)

Question 2.
What would happen if five times this number sat in your class?
Answer:
If five times this number sat in my class, the classroom would be crowded. There will be utter chaos.

Question 3.
Which kind of disaster can occur in an extremely crowded places?
Answer:
In an extremely crowded place there can be panic in the classroom, stampede while going out of the classroom, breathless among fellow students.

Maharashtra State Board Class 6 Science Textbook Solutions

• Natural Resources – Air, Water and Land Class 6 Science Textbook Solutions
• The Living World Class 6 Science Textbook Solutions
• Diversity in Living Things and their Classification Class 6 Science Textbook Solutions
• Disaster Management Class 6 Science Textbook Solutions
• Substances in the Surroundings – Their States and Proper Class 6 Science Textbook Solutionsties
• Substances in Daily Use Class 6 Science Textbook Solutions
• Nutrition and Diet Class 6 Science Textbook Solutions
• Our Skeletal System and the Skin Class 6 Science Textbook Solutions
• Motion and Types of Motion Class 6 Science Textbook Solutions
• Force and Types of Force Class 6 Science Textbook Solutions

Std 7 Science Chapter 3 Properties of Natural Resources Question Answer Maharashtra Board

Balbharti Maharashtra State Board Class 7 Science Solutions Chapter 3 Properties of Natural Resources Notes, Textbook Exercise Important Questions and Answers.

Class 7 Science Chapter 3 Properties of Natural Resources Question Answer Maharashtra Board

Fill in the blanks with the appropriate term.

Question 1.
The capacity of air to hold moisture depends upon the …………… of the air.
Answer:
temperature

Question 2.
Water does not have a …………… but has definite ………… and ………. .
Answer:
shape, volume, mass

Question 3.
While freezing, the ………….. of water is lowered.
Answer:
density

Question 4.
…………….. soil has pH 7.
Answer:
neutral

2. Why is the said that –

Question a.
Air is a homogeneous mixture of various gases.
Answer:

1. Air is made of oxygen, nitrogen, carbondioxide, water vapour and dust particles.
2. All these are in different proportions. Therefore air is a mixture.

Question b.
Water is a universal solvent.
Answer:

1. Water dissolves more substances than any other liquid. It dissolves solids, other liquids and even gases in it. Therefore, it is called as Universal solvent.
2. Water is used as a solvent in factories, laboratories, foodstuffs and in various types of biological processes occurring in the body such as digestion, excretion, etc.

Question c.
There is no alternative to water for cleaning purposes.
Answer:
Water is a universal solvent. It dissolves more substances than any other liquid so there is no alternative to water for cleaning purposes.

3. What will happen if……

Question a.
The amount of water vapour in the air increases.
Answer:
We feel the dampness or the humidity.

Question b.
Only one crop is grown repeatedly in the soil.
Answer:
The fertility of the soil decreases.

4. With whom should I pair up? 

Question a.

Answer:

5. State whether the following statements are true or false.

Question a.
Sandy soil has low capacity for holding water.
Answer:
True

Question b.
Sea water is a bad conductor of electricity.
Answer:
False. Sea water is a good conductor of electricity

Question c.
The substance in which a solute dissolves is called a solvent.
Answer:
True

Question d.
The pressure exerted by air is called atmospheric pressure.
Answer:
True

6. Explain the picture in your own words. 

Question a.
Explain the picture in your own words.

Answer:

• Diagram (a): Water is filled in the crack.
• Diagram (b): Water in the crack turns to ice due to decrease in temperature. When it turns to ice the volume increases and it expands. Due to expansion, the size of crack widens more than in diagram (a).

 7. Write answers to the following questions in your own words. 

Question a.
How is light scattered by the air?
Answer:
Air is a mixture of very fine particles of some gases, dust, smoke and moisture. When rays of light fall on these minute particles, the particles spread the light in all the directions. This natural phenomenon is called scattering of light.

Question b
Explain the various properties of water.
Answer:
Various properties of water are as follows:

1. It is a fluid substance because it can flow.
2. It does not have its own shape, it takes the shape of a container in which it is kept.
3. It has a definite volume.
4. It is a transparent liquid and it has no colour.
5. It is tasteless and odourless.
6. It is a universal solvent.

Question c.
Why is the density of seawater is more than that of rainwater?
Answer:
Seawater has many minerals dissolved in it as compared to rainwater. So due to more dissolved salts, density of seawater is more than that of rainwater.

Question d.
What is the importance of good soil structure?
Answer:
The fertility of soil depends upon soil structure. So importance of good soil structure is as follows: (a) Roots get sufficient supply of oxygen, (b) Water drainage is good therefore the roots of plants grow well.

Question e.
What are the various uses of soil?
Answer:
The uses of soil are as follows:
Plant conservation: To help plants grow. Water conservation: Soil holds water. As a result, by means of bunds and lakes, we can get water for use throughout the year.
Plasticity: (a) Soil can be given any required shape. This property of soil is called plasticity, (b) Because of its plasticity, we can use it to make articles of a variety of shapes, (c) These articles can be baked to make them hard, (d) Water storage earthen pots, earthen lamps, idols, bricks etc. are articles made from soil.

Question f.
What is the need and importance of soil testing from the point of view of farmers?
Answer:

1. The properties of the various ingredients of soil can be determined by soil testing.
2. During soil testing, the soil is examined for colour, texture and the proportion of organic matter in it.
3. Soil is tested to find out if there is a deficiency of any ingredients and to decide what measures should be taken to remove the deficiency. These information would enable the farmers to maintain the fertility of the soil.

Question g.
What is the importance of air in transmission of sound?
Answer:

1. Air is useful as a medium for the transmission of sound. Density of the air changes with temperature.
2. If the density of air increases, we can hear the sound more loud and clear.

Question h.
Why should a glass bottle completely filled with water never be kept in a freezer?
Answer:

1. Due to anomalous behaviour of water, when you cool water below 4°C, the volume of the water increases.
2. Therefore when the glass bottle completely filled with water is kept in a freezer, water expands on cooling and its volume increases so glass bottle breaks.
3. To avoid this, completely filled bottle is never kept in a freezer.

Project:

Question a.
Visit a soil testing laboratory. Learn the process of soil testing and share it with others.

Class 7 Science Chapter 3 Properties of Natural Resources Important Questions and Answers

Fill in the blanks with the appropriate term.

Question 1.
Air is a …………… of gases.
Answer:
mixture

Question 2.
Atmospheric pressure is the …………… in all the directions.
Answer:
same

Question 3.
…………… is used to measure atmospheric pressure.
Answer:
Barometer

Question 4.
As we go higher the sea level and the atmospheric pressure …………… .
Answer:
decreases

Question 5.
Pressure of air …………… when its velocity …………… .
Answer:
increases, decreases

Question 6.
…………… an effect of the difference in air pressure.
Answer:
Wind

Question 7.
The level of …………… in the air is determined by its capacity to hold water vapour.
Answer:
humidity

Question 8.
When the temperature of air is low, its capacity to hold the vapour is …………… .
Answer:
less

Question 9.
Air is useful as a …………… for the transmission of sound.
Answer:
medium

Question 10.
Water is a …………… substance.
Answer:
fluid

Question 11.
Ice is …………… than water.
Answer:
lighter

Question 12.
Density of ice is …………… than that of water.
Answer:
less

Question 13.
The space occupied by a substance is its …………… .
Answer:
volume

Question 14.
The storage of matter in a substance is its …………… .
Answer:
mass

Question 15.
The density of water is maximum at …………… °C.
Answer:
4°C

Question 16.
The substance in which the solute dissolves is called …………… .
Answer:
solvent

Question 17.
The particles of sandy soil are made of the mineral called …………… .
Answer:
silicon dioxide (quartz)

Question 18.
…………… soil has a highest water holding capacity.
Answer:
clay

Question 19.
…………… soil is red in colour.
Answer:
Terracotta

Question 20.
…………… soil is used in cosmetics.
Answer:
Multani

Question 21.
…………… is celebrated as World Soil Day.
Answer:
5th December

Question 22.
The excess of water vapour during the night or dawn is transformed into ………….. .
Answer:
dew

Question 23.
Under ordinary conditions atmospheric pressure at sea level is …………… Newtons per square mater.
Answer:
101400

Question 24.
Swedish Scientist …………… put forth the important principle that the pressure of air decreases when its velocity increases.
Answer:
Daniel Bernoulli

Question 25.
When rays of light fall on fine particles of air, the particles spread light in all the directions, this is called …………… of light.
Answer:
Scattering

Question 26.
…………… soil is easy to plough but less fertile.
Answer:
Sandy

Say whether true or false, correct and rewrite the false statements.

Question 1.
Terracotta soil is white in colour.
Answer:
False. Terracotta soil is red in colour

Question 2.
The fertility of soil depends upon soil structure.
Answer:
True

Question 3.
Multani soil is used to make statues and idols.
Answer:
False. Shadu soil is used to make statues and idols

Question 4.
Clay soil has the maximum proportion of small particles.
Answer:
True

Question 5.
Silt soil is not as ploughable as sandy soil.
Answer:
True

Question 6.
The colour of soil near land surface is darker than the colour of the lower layers.
Answer:
True

Question 7.
Kerosene is a universal solvent.
Answer:
False. Water is an universal solvent

Question 8.
The density of substance is the inter-relation between the volume and mass of a substance.
Answer:
True

Question 9.
Water is lighter than ice.
Answer:
False. Ice is lighter than water

Question 10.
Rotation of crops decreases the fertility of the soil.
Answer:
False. Rotation of crop increases the fertility of the soil.

Match the columns:

Question 1.

Answer:

Write short answers.

Question 1.
What is atmospheric pressure?
Answer:
The molecules of the gases in the air are in constant motion. When these molecules strike a body, they create pressure on that body. This pressure of air is called atmospheric pressure.

Question 2.
What is Bernoulli’s principle?
Answer:
Bernoulli’s principle is that the pressure of air ‘ decreases when its velocity increases while the pressure of air increases when its velocity decreases.

Give scientific reasons.

Question 1.
When the piston of a syringe is released, it is immediately pushed in.
Answer:

1. On pulling the piston of a syringe with the inlet hole of the syringe closed, more space becomes available to the air in the syringe, and it becomes rarified.
2. As a result, the pressure of the air in the syringe is lowered.
3. Comparatively the pressure of the outside air is very high. So when the pulled out piston is A released, it is immediately pushed in.

Question 2.
Water droplets are seen on the outer surface of a glass having ice cubes in it.
Answer:

1. Due to the ice cubes in the glass, the air surrounding the glass cools down.
2. As the water vapour in this air cools down, it condenses and gets transformed into water.
3. It is this water that collects on the outer surface of the glass.

Question 3.
Early morning dew drops are found on the grass.
Answer:

1. During the dawn (early morning) when the temperature of air is low, its capacity to hold the vapour is less.
2. At such times, the excess vapour is transformed into water droplets and we call them as dew drops.

Question 4.
During the afternoon we feel that the air is dry.
Answer:

1. In the afternoon, when the temperature of the air is high, the capacity of the air to hold the moisture also increases.
2. Then, compared to its full capacity to hold water the proportion of moisture in the air is less and we feel that the air is dry.

Question 5.
Earth’s surface remains warm and suitable for the living world on the earth.
Answer:

1. The earth receives energy from the sun. This energy is reflected by the earth in the form of heat.
2. The constituents of air surrounding the earth, such as water vapour, carbon dioxide, absorb a part of this heat and give it to the other constituents of air.
3. So the Earth’s surface remains warm and suitable for the living world on the earth.

Question 6.
We can hear the whistle of a distant train clearly early in the morning in winter.
Answer:

1. The density of air changes due to change in its temperature.
2. In winter, temperature is low so the density of the air is more. So we can hear the whistle of a distant train clearly early in the morning in winter.

Question 7.
Ice floats on water.
Answer:

1. When water freezes means it transforms into the soild state therefore its volume increases.
2. When volume increases its density decreases
3. Therefore, density of ice is less than the water, so ice floats on water.

Question 8.
In cold countries aquatic animals remain alive even after the rivers or lakes freeze in water.
Answer:
1. Due to anomalous behaviour of water, in cold countries when water gets cool and turn to ice, its volume increases, so its density decreases
2. Due to less density ice floats on water.
3.  (a) Ice is a bad conductor of heat and electricity, (b) It doesn’t allow outside heat to go from the ice to water so water temperature below the ice doesn’t change, (c) It remains as water so aquatic animals remain alive even after the rivers or lakes freeze in winter.

Question 9.
It is easier to swim in the sea than in a well or a lake.
Answer:

1. Sea water is saline. It contains salt whereas it is not so in well or a lake water.
2. Due to salts dissolved in sea water, density of sea water is more, so the swijnmer will not sink.
3. Hence, it is easier to swim in the sea than in a well or a lake.

Question 10.
Sandy soil is less fertile.
Answer:

1. Sandy soil is made up of large particles and these particles of sandy soil are made of the mineral called silicon dioxide.
2. These particles do not dissolve in water therefore soil has very little capacity to supply nutrients, so sandy soil is less fertile.

Question 11.
China clay is used for making crockery.
Answer:
China clay is used for making crockery because on heating, this clay acquires a glaze and hardness. It can be moulded into any shape and being a bad conductor of heat, it is easy to handle.

Answer the following:

Question 1.
Write the properties of air.
Answer:

1. Air is a mixture of gases.
2. Air has mass and volume.
3. It spreads in all directions.
4. It exerts pressure.
5. It is colourless.

Question 2.
Name the tests for finding out the characteristic of soil. Describe any one method of it.
Answer:
There are two tests for finding out the characteristics of soil: (1) pH (2) electrical conductivity tests.
1. pH tests: The Danish scientist Sorensen put forth the concept of pH, based on the concentration of hydrogen ions. To determine the pH of soil, a mixture of water and soil in the proportion of 1 : 2 is taken and tested using several indicators.
Accordingly, soil may be found to be one of the following types.

• Acidic soil – pH less than 6.5
• Neutral soil – pH 6.5 – 7.5
• Alkaline soil – pH higher than 7.5

2. By Electrical conductivity tests we come to know how many nutrients are present in the soil.

Question 3.
Write the causes of diminished soil fertility.
Answer:
Following are the causes of diminished soil fertility.

1. Soil pH less than 6 or higher than 8.
2. Low proportion of organic matter.
3. No proper drainage of water.
4. Repeated cultivation of the same crop.
5. Continuous use of saline water.
6. Excessive use of chemical fertilizers and pesticides.

Question 4.
Which crops reduce the fertility of soil and Which crops increase the fertility of soil?
Answer:
Wheat reduces the fertility of soil and leguminous crops like peanut, moong, moth bean, pea, lentil, Bengal gram, soyabean increase the fertility of soil.

Question 5.
Name and explain some useful types of soil.
Answer:
Following are some useful types of soil.

1. China clay (Kaolin): (a) It is white in colour, (b) It is used to make crockery, bathroom tiles, tanks, laboratory apparatus, masks, jars etc.
2. Shadu soil: (a) It is whitish in colour, (b) It is used for making statues and idols.
3. Terracotta soil: (a) This soil is red in colour, (b) Decorative articles and pots used for growing plants are made from this soil.
4. Multani soil: This soil is used in cosmetics.

Question 6.
Explain the types of soil on the basis of its texture.
Answer:
There are 3 types of soil on the basis of its texture.
1. Sandy soil: (a) Large particles are high in sandy soil, (b) Water drains rapidly through sandy soil, (c) It is easy to plough this soil, (d) It is less fertile because the particles of sandy soil are made of the mineral called silicon dioxide (quartz), (e) These particles do not dissolve in water and therefore the soil has very little capacity to supply dissolved nutrients.

2. Silt soil: (a) The particles of silt soil are of medium size, (b) Silt soil is not as ploughable as sandy soil but is much more ploughable than clay soil, (c) This soil contains a large proportion of organic materials, (d) Its capacity to supply nutrients is much greater, (e) Silt soil is also called sedimentary soil.

3. Clay soil: (a) The proportion of small particles is maximum, (b) The particles of clay soil feel smooth to touch, (c) Clay soil has a high water holding capacity.

Explain the given picture in your own words.

Question 1.

Answer:
1. The potato will sink in water as potato’s density is more than water.
2. This is the effect of density. The potato will float in salt solution as the density of salt solution is more than potato. The density of the water becomes greater due to the dissolved salt. That is why it is easier to swim in sea than in a well or a lake.

Can you tell?

Answer the following questions.

Question 1.
What change takes place in a balloon on filling air in it?
Answer:
On filling air in balloon, the shape of the balloon changes. Its size increases due to expansion.

Question 2.
Why is it easier to swim in the sea than in a well or a lake?
Answer:

1. Sea water is salty due to minerals in it. Whereas it is absent in well or a lake water.
2. Due to presence of salts, density of seawater is more than well or lake water, so it is easier to swim in the sea than in a well or lake.

Use your brain power!

Answer the following questions.

Question 1.
What is the effect of increased temperature on the pressure of air?
Answer:
Condition for closed environment:

1. When the temperature increases, the pressure of air also increases.
2. For example, as the air warms up, the molecules in the air become more active.
3. They use up more individual space even though there is same number of molecules. T1 s causes an increase in the air pressure.

Question 2.
Dip an uncorked inverted empty bottle in a slanting position into the water in a wide container. What do you observe?

Answer:

1. When an uncorked inverted empty bottle is kept slanting in the water container bubbling sound will be heard.
2. Air bubbles come out from the empty bottle and water enters the bottle.
3. Empty bottle is actually not empty but it is occupied by air.
4. When this air comes out, its place is taken by water. This shows that air occupies space.

Question 3.
In cold countries how do aquatic animals remain alive even after the rivers or lakes freeze in winter.
Answer:

1. Due to anomalous behaviour of water, in cold countries, water changes to ice.
2. Due to this change, its volume increases and density decreases. So ice floats on water.
3. Ice is a bad conductor of heat so it doesn’t allow heat to go inside so the water below ice remains as it is. So aquatic animals remain alive even after the rivers or lakes freeze in winter.

Question 4.
Why is it difficult to plough clay soil?
Answer:
It is difficult to plough clay soil because in clay soil the proportion of small particles is maximum. The particles of clay soil feel smooth to touch and has high water holding capacity, making it very difficult to penetrate through it.

Question 5.
Why is it easy to plough sandy soil?
Answer:

1. Sandy soil has large sized particles. It has weak structure due to less organic matter and large spaces between them.
2. The water also drains quickly through it making it dry and allows the plough to penetrate through it.

Question 6.
What is the water holding capacity of silt soil?
Answer:
Silt occurs as a deposit in riverbeds. The size of silt particles is between those of sand and clay. This soil also has humus in it which makes it the best soil to hold the right amount of water.

Question 7.
Which soil is suitable for cultivation? Why?
Answer:
The silt soil is suitable for cultivation.

1. The particles of silt soil is of medium size.
2. Silt soil is much more ploughable than clayey soil.
3. It contains large proportions of organic material.
4. This helps the soil in retention of water for a proper amount of time and makes it suitable for crops to grow.

Maharashtra State Board Class 7 Science Textbook Solutions

• The Living World: Adaptations and Classification Class 7 Science Textbook Solutions
• Plants: Structure and Function Class 7 Science Textbook Solutions
• Properties of Natural Resources Class 7 Science Textbook Solutions
• Nutrition in Living Organisms Class 7 Science Textbook Solutions
• Food Safety Class 7 Science Textbook Solutions
• Measurement of Physical Quantities Class 7 Science Textbook Solutions
• Motion, Force and Work Class 7 Science Textbook Solutions
• Static Electricity Class 7 Science Textbook Solutions
• Heat Class 7 Science Textbook Solutions
• Disaster Management Class 7 Science Textbook Solutions

Std 8 Science Chapter 14 Measurement and Effects of Heat Question Answer Maharashtra Board

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 14 Measurement and Effects of Heat Notes, Textbook Exercise Important Questions and Answers.

Class 8 Science Chapter 14 Measurement and Effects of Heat Question Answer Maharashtra Board

Class 8 Science Chapter 14 Measurement and Effects of Heat Textbook Questions and Answers

1. A. Whom should I pair with?

Question a.

Answer:

B. Who is telling the truth?

Question a.
The temperature of a substance is measured in joule.
Answer:
False. (The temperature of a substance is measured in °C or °F or K.)

Question b.
Heat flows from an object at higher temperature to an object at lower temperature.
Answer:
True.

Question c.
The joule is the unit of heat.
Answer:
True.

Question d.
Objects contract on heating.
Answer:
False. (In general, objects expand on heating. There are some exceptions to this, you will learn about them in Standard X.)

Question e.
Atoms of a solid are free.
Answer:
False. (Atoms of a solid are bound to each other due to the forces acting between them.)

Question f.
The average kinetic energy of atoms in a hot object is less than the average kinetic energy of atoms in a cold object.
Answer:
False. (The average kinetic energy of atoms in a hot object is more than the average kinetic energy of atoms in a cold object.)

C. You will find if you search.

Question a.
A thermometer is used to measure ……………. .
Answer:
A thermometer is used to measure temperature.

Question b.
The apparatus used to measure heat is called a ………… .
Answer:
The apparatus used to measure heat is called a calorimeter.

Question c.
Temperature is the measure of the …………. kinetic energy of the atoms in a substance.
Answer:
Temperature is the measure of the average kinetic energy of the atoms in a substance.

Question d.
The heat contained in a substance is the measure of the ………….. kinetic energy of the atoms in the substance.
Answer:
The heat contained in a substance is the measure of the total kinetic energy of the atoms in the substance.

2. Nishigandha kept a vessel containing all the ingredients for making tea in a solar cooker. Shivani kept a similar vessel on a stove. Whose tea will be ready first and why?

Question a.
Nishigandha kept a vessel containing all the ingredients for making tea in a solar cooker. Shivani kept a similar vessel on a stove. Whose tea will be ready first and why?
Answer:
Shivani’s tea will be ready first.
Reason: In a given time, the amount of heat received by the vessel on a stove is far greater than that received by the vessel kept in a solar cooker.

3. Write brief answers.

Question a.
Describe a clinical thermometer. How does it differ from the thermometer used in a laboratory?
Answer:
A clinical thermometer has a narrow stem and a long bulb filled with mercury (or alcohol). There is a small constriction in the stem above the bulb. When the bulb of the thermometer is held in the armpit or the mouth of a patient, the mercury (or alcohol) in the bulb rises in the stem.

When it is taken out of the patient’s body, the small constriction does not allow the mercury (or alcohol) from the stem to retreat into the bulb. Thus, this arrangement enables us to read the temperature of the patient’s body at ease after the removal of the thermometer from his body.

The clinical thermometer is graduated from 35 °C to 42 °C (or from 95 °F to 108 °F). At 37 °C (98.6 °F), there is a red arrow mark which indicates the temperature of a healthy person.

The thermometer used in a laboratory has wider range and does not have constriction like a clinical thermometer.

Question b.
What is the difference between heat and temperature?
Answer:
Heat is related to the total kinetic energy of the atoms in a substance while temperature is related to the average kinetic energy of the atoms in the substance. Heat flows from a body at higher temperature to a body at lower temperature. Thus, temperature is a quantity that determines the direction of flow of heat. It is a quantitative measure of the degree of hotness or coldness of a body.

Higher temperature does not mean higher heat content. Suppose a vessel A contains 2 litres of water at 90 °C and a vessel B contains 100 ml of water at 91 °C. Then the heat content of water in A is greater than that of water in B, but the temperature of water in B is higher than that of water in A.

Units of heat:
Heat is usually expressed in calorie, kilocalorie and joule. It can also be expressed in erg as heat is a form of energy.

Question c.
Explain the construction of a calorimeter. Draw the necessary figure.
Answer:

Figure shows the construction of a calorimeter. Like a thermo flask, a calorimeter has two vessels. The inner vessel, made of copper, is (practically) thermally isolated from the surroundings. The outer vessel is made of wood and is covered with a heat resistant lid. The lid has two holes, one for the thermometer and the other for the stirrer. The inner and outer surfaces of the inner vessel are polished for minimizing exchange of heat with the surroundings by radiation. A heat resistant ring covers the inner vessel.

Question d.
Explain why rails have gaps at specific distances.
Answer:
The rails expand in summer due to increase in the temperature of the atmosphere. Also, they expand due to rise in temperature caused by the friction between the rails and the wheels of the running train. If there is no gap between successive rails of a railway line, the rails would bend due to expansion. This bending and twisting of the rails would cause accidents. Hence, a gap is kept between successive rails of a railway line to make provision for their expansion in summer.

Do you know:

Have you seen rails? They are not continuous. A small gap is kept between them at regular intervals. This is shown in the figure. This is kept to accommodate the change in the length of the rails with change in temperature. If this gap is not kept, then the rail will get distorted due to expansion in summer which may lead to accidents.

Similar to rails, the length of bridges can also increase due to expansion in summer. The length of the 18 km long great belt bridge in Denmark increases by 4.7 m in summer. Therefore, provision in made in the construction of the bridges to accommodate this expansion.

Question e.
Explain with the help of formulae the expansion coefficients of liquid and gas.
Answer:
1. A liquid is held in a container. When it is heated, both the container and the liquid expand. The expansion of the container is usually very small compared to that of the liquid in it. Often, it can be ignored.
Suppose a liquid is heated so that its temperature rises by ΔT (very small) and its volume increases from V₁ to V₂. Experimentally, it is found that the increase in volume, V₂ – V₁, is proportional to V₁ and ΔT.
Hence, (V₂ – V₁) α V₁ΔT.
∴ V₂ – V₁ = β V₁ΔT, where β is a constant of proportionality called the volumetric expansion coefficient of the liquid.
β = \(\frac{V_{2}-V_{1}}{V_{1} \Delta T}\).
It is expressed in per °C.
We have V₂ = V₁ + βV₁ΔT = V₁(1 + β ΔT).
β is the increase in the volume of a liquid per unit original volume per unit rise in its temperature.

2. A gas is enclosed in a container. When it is heated at constant pressure, both the container and the gas expand. Suppose a gas is heated at constant pressure so that its temperature rises by ΔT (very small) and its volume increases from V₁ to V₂. Experimentally, it is found that the increase in volume, V₂ – V₁ is proportional to V₁ and ΔT. Hence, (V₂ – V₁) a V₁ΔT.
∴ V₂ – V₁ = β V₁ΔT, where β is a constant of proportionality, the volumetric expansion coefficient, called the constant pressure expansion coefficient.
β = \(\frac{V_{2}-V_{1}}{V_{1} \Delta T}\).
It is expressed in per °C.
We have V₂ = V₁ + βV₁T = V₁(1 + β ΔT).
β is the increase in the volume of a gas per unit original volume per unit rise in its temperature when the pressure is kept constant.

4. Solve the following examples.

Question a.
What must be the temperature in Fahrenheit so that it will be twice its value in Celsius?
Solution:
Data: F = 2 C ∴ C = F/2, F = ?

∴ F – 0.9 F = 32
∴ 0.1 F = 32
∴ F = \(\frac{32}{0.1}\) = 320 °F.

Question b.
A bridge is made from 20 m long iron rods. At temperature 18 °C, the distance between two rods is 0.4 cm. Up to what temperature will the bridge be in good shape?
Solution:
Data: l₁ = 20 m, l₂ – l₁ = 0.4 cm
= 4 × 10^-3 m, T_i = 18 °C, λ for iron = 11.5 × 10^-6/°C
l₂ – l₁ = λl₁ Δt

= \(\frac{400}{23}\) °C = about 17.39 °C
Now, ΔT= T_f – T_i ∴ T_f = T_i + ΔT
∴ T_f = 18 °C + 17.39 °C = 35.39 °C.
The bridge will be in good shape up to 35.39 °C.

Question c.
At 15 °C the height of Eiffel Tower is 324 m. If it is made of iron, what will be the increase in length in cm, at 30 °C?
Solution:
Data: ΔT = 30 °C – 15 °C = 15 °C, l₁ = 324 m, λ for iron = 11.5 × 10^-6/°C l₂ – l₁ = λl₁ ΔT
= 11.5 × 10^-6/°C × 324 m × 15 °C
= 55890 × 10^-6 m
= 55890 × 10^-6 × 10² cm
= 55890 × 10^-4 cm
= 5.589 cm (nearly 5.6 cm)
This is the increase in the length, i.e., the increase in the height of Eiffel Tower.

Question d.
Two substances A and B have specific heats c and 2 c respectively. If A and B are given Q and 4Q amounts of heat respectively, the change in their temperatures is the same. If the mass of A is m, what is the mass of B?
Solution:
Data: c (A) = c, c (B) = 2c,
Q (A) = Q, Q (B) = 4Q, ΔT same,
m (A) = m, m (B) = ?

∴ m(B) = 2m.
This is the mass of B.

Question e.
When a substance having mass 3 kg receives 600 cal of heat, its temperature increases by 10 °C. What is the specific heat of the substance?
Solution:
Data: m = 3 kg = 3000 g,
Q = 600 cal, ΔT = 10 °C, c = ?
Q = mcΔT

= 0.02 cal/(g.°C)
This is the specific heat of the substance.

Can you recall?

Question a.
Which sources do we get heat from?
Answer:

1. Sun
2. earth
3. fuels like wood, coal, petrol
4. electricity
5. atomic energy
6. air.

Question b.
How is heat transferred?
Answer:
Heat is transferred by conduction, convection and radiation.

Question c.
Which effects of heat do you know?
Answer:
Expansion, change of state, rise in temperature, emission of light, burning.

Question d.
Some effects of heat are shown in Fig. What are they?

Answer:
Rise in temperature/boiling, melting, burning, expansion.

Question e.
What are potential and kinetic energies?
Answer:
The energy stored in a body because of its specific state or position is called its potential energy. The energy possessed by a body because of its motion is called it’s kinetic energy.

Project:

Question a.
Collect information about bimetallic strips and discuss in your class how a fire alarm is made using it.

Class 8 Science Chapter 14 Measurement and Effects of Heat Important Questions and Answers

Rewrite the following statements by selecting the correct options:

Question 1.
32°F is equal to …………….. .
(a) 212 °C
(b) 212 K
(c) 273.15 K
(d) 273.15 K
Answer:
32°F is equal to 273.15 K.

Question 2.
-40°C is equal to ………….. .
(a) -40 °F
(b) 40 °F
(c) -8°F
(d) 40K
Answer:
-40°C is equal to -40 °F.

Question 3.
The boiling point of water is ………… .
(a) 212 K
(b) 212 °F
(c) 273.15 K
(d) 32 °F
Answer:
The boiling point of pure water is 212 °F.

Question 4.
Specific heat is expressed in …………… .
(a) J/(kg. °C)
(b) kg/(J C)
(c) J/kg
(d) cal/g
Answer:
Specific heat is expressed in J/(kg.°C).

Question 5.
The freezing point of water is …………….. .
(a) OK
(b) 212°F
(c) 32°F
(d) 0°F
Answer:
The freezing point of water is 32 °F.

Find the odd one out and give the reason:

Question 1.
0°C, 32°F, 273.15K, 212°F.
Answer:
212 °F. This is the boiling point of water; others correspond to the freezing point of water.

Question 2.
373.15 K, 100 °C, 212 °F, 32 °F.
Answer:
32 °F. This is the freezing point of water others correspond to the boiling point of water.

Answer the following questions in one sentence each:

Question 1.
Name the biggest source of heat received by the earth.
Answer:
The Sun is the biggest source of heat received by the earth.

Question 2.
What is the relation between the temperature in °C and the temperature in °F?
F – 32 °C
Answer:
\(\frac{F-32}{9}\) = \(\frac{C}{5}\), where C denotes temperature in °C and F denotes temperature in °F.

Question 3.
Name the quantity expressed in cal/(g.°C).
Answer:
Specific heat is expressed in cal/(g.°C).

Question 4.
State the formula for the coefficient of linear expansion of a solid substance.
Answer:
λ = (l₂ – l₁]) / (l₁ ΔT).

Question 5.
State the formula for the coefficient of areal expansion of a solid.
Answer:
σ = (A₂ – A₁)/ (A₁ ΔT).

Question 6.
State the formula for the volumetric expansion coefficient of a solid.
Answer:
β = (V₂ – V₁) / (V₁ ΔT).

Question 7.
State the relation between λ and σ (if ΔT is very small).
Answer:
σ = 2 λ.

Answer the following questions:

Question 1.
How is heat generated in the Sun?
Answer:
In the interior of the Sun, at the centre, hydrogen nuclei fuse together to form helium nuclei. A lot of heat is generated in this process.

Question 2.
What is geothermal energy?
Answer:
Heat within the interior of the earth, e.g., that coming from the molten core of the earth, is called geothermal energy.
[Note: Volcanoes, geysers, hot springs are sources of this energy.]

Question 3.
What is atomic energy or nuclear energy?
Answer:
Energy released or obtained in nuclear fission or nuclear fusion is called atomic energy or nuclear energy.

Question 4.
Name three sources of chemical energy.
Answer:
Fuels like wood, coal and petrol are sources of chemical energy.

Try this:

1. Take three similar vessels. Let us call them ‘A’, ‘B’ and ‘C’.
2. Fill A with hot water and B with cold water. Put some water from A and B in C.
3. Dip your right hand in A and left hand in B and keep them immersed for 2 to 3 minutes.
4. Now dip both the hands in C. What do you feel?

Even though, both the hands are dipped in water in the same vessel, i.e., water at the same temperature, your right hand will find the water to be cold while the left hand will find it to be hot. What is the reason for this? Think about it.
Answer:
The right hand finds the water cold because it loses heat to water in C. The left-hand feels the water hot because it gains heat from water in C. (This shows that we cannot determine the temperature of an object accurately by simply touching it)

Question 5.
State the units in which temperature is expressed.
OR
What are the units of temperature?
Answer:
Temperature is expressed in °C (degree Celsius), °F (degree Fahrenheit) and K (kelvin).

Question 6.
Draw diagrams to illustrate motion of atoms in a gas and a solid. Also explain the type of motion.
Answer:
Atoms of a gas are comparatively free and move at random. Figures a and b show the velocities of atoms in a gas at high and low temperature, respectively. The direction and the length of the arrows show respectively the direction and the magnitude of the velocity of the atoms. The velocity of atoms in the gas at higher temperature is larger in magnitude than the velocity of atoms in the gas at lower temperature.

The velocities of atoms in a solid are shown by arrows in Fig. (c). The atoms in a solid are tied to one another because of the forces acting between them. This is indicated by drawing springs between adjacent atoms. Because of heat, they oscillate around their fixed mean positions. The higher the temperature of a solid, the greater is their velocity of oscillation.

Try this:

1. Take two steel vessels A and B of the same size.
2. Fill some water in A and double that amount in B. Make sure that the water in both vessels is at the same temperature.
3. Raise the temperatures of water in both vessels by 10 CC using a spirit lamp. Did it take the same time to increase the temperature in the two vessels?
Answer:
No.
You must have required more time to raise the temperature of water in B. This means that for the same increase in temperature, you had to give more amount of heat to B. Thus, even though the water in A and in B have the same temperature, the amount of heat in B is more than that in A.

Question 7.
How are the different units of temperature-related?
Answer:
1. The SI unit of temperature is the kelvin (K). Temperature is also expressed in °C (degree Celsius) and °F (degree Fahrenheit).

Here, C denotes temperature in °C, F denotes temperature in 0F and K denotes temperature in K (kelvin).
[Notes: (i) The unît degree Celsius is named in honour of Anders Celsius (1701 – 44) Swedish astronomer. He devised a temperature scale in 1742.
(ii) The unit degree Fahrenheit is named in honour of Gabriel Daniel Fahrenheit (1686 – 1736) German physicist. He developed the mercury thermometer and devised the temperature scale.
(iii) The unit kelvin is named in honour of William Thomson, 1st Baron Kelvin (of Largs) (1824 – 1907) British physicist and electrical engineer. He made significant contribution in thermodynamics and electromagnetic theory. He proposed a scale of temperature now known as the Kelvin scale or thermodynamic scale.]

Question 8.
What is a liquid (mercury or alcohol) thermometer?
Answer:
A thermometer in which the change in the volume of a liquid (mercury or alcohol) with temperature is used for measurement of temperature is called a liquid thermometer.

Question 9.
Why has mecury been replaced by alcohol in a thermometer?
Answer:
Because mercury is harmful for us, it has been replaced by alcohol in a thermometer.
[Notes: (i) Mercury thermometers are still widely used in laboratories in schools and colleges.
(ii) A thermometer is a device to measure temperature. A thermometer containing mercury in its bulb is called a mercury thermometer. There are other types of thermometer such as a thermocouple thermometer, a platinum resistance thermometer, a thermistor thermometer, etc.]

Question 10.
Describe the construction of mercury thermometer.
Answer:

1. For constructing a thermometer, a thick-walled capillary tube with a uniform bore is taken. The tube has a thin-walled glass bulb at one end.
2. The bulb and a small part of the tube is filled with mercury. The other end of the tube is sealed after removing air from it.
3. The tube is then calibrated and the temperature of the substance can be read with it.

[Note: The range of an alcohol thermometer is different from that of a mercury thermometer.]

Question 11.
How does a mercury thermometer work?
Answer:
1. When the bulb of the thermometer is brought in contact with the substance whose temperature is to be measured, there is an exchange of heat between the substance and the mercury in the bulb.

2. The mercury expands or contracts depending upon whether it gains heat or loses heat. Accordingly there is a rise or fall of the level of mercury in the tube of the thermometer indicating the temperature of the substance when the mercury and the substance are in thermal equilibrium.

Question 12.
Why is the bore of a thermometer made very small?
Answer:
The bore of a thermometer is made very small so that even a slight variation in the temperature may cause noticeable variation in the mercury level in the tube of the thermometer. As a result, the sensitivity of the thermometer increases and even small changes in the temperature can be recorded.

Question 13.
Why does the bulb of a thermometer have a thin glass wall?
Answer:
The bulb of a thermometer is made of a thin glass so that it can easily conduct the heat from the substance in contact with the mercury in the bulb.

Question 14.
Why does a thermometer usually break at the bulb?
Answer:
The bulb of a thermometer has a thin glass wall. Therefore, a thermometer usually breaks at the bulb.

Question 15.
Explain why the capillary tube of a clinical thermometer has a constriction.
Answer:
When the temperature of a patient is measured with a clinical thermometer, the mercury in the bulb expands and rises in the tube. The small constriction in the thermometer prevents the mercury thread from retreating into the bulb. Thus, the patient’s temperature can be read at ease after removing the thermometer from his body.

Question 16.
Explain why a clinical thermometer should not be washed with hot water.
Answer:
A clinical thermometer is constructed for the purpose of recording the temperature of the human body. Hence, its stem is such that it can allow the mercury to rise up to a temperature of about 42 °C. The temperature of hot water may be more than 42 °C. Therefore, when a clinical thermometer is washed with hot water, mercury will not have enough room for expansion and the thermometer would break.

[Note: (1) A digital thermometer has a sensor that detects the heat coming out from the body directly and displays the temperature.
(2) The maximum-minimum temperature has two scales, one against each arm of the thermometer. One scale indicates the maximum temperature reached (generally during the day) and the other scale indicates the minimum temperature reached (generally during the night).]

Question 17.
Explain what happens when there is exchange of heat between two objects.
Answer:
When there is an exchange of heat between a hot object and a cold object, the temperature of the hot object falls and the temperature of the cold object rises. If this system of two objects is isolated from the surroundings so that no heat enters or leaves the system, then, heat lost by the hot object = heat gained by the cold object. After some time, the average kinetic energies of the atoms in the two objects become equal, i.e., the two objects attain the same temperature.

Question 18.
Define specific heat.
Answer:
The specific heat of an object (substance) is the amount of heat required to increase the temperature of unit mass of that substance through one degree.

Question 19.
Write the formula for specific heat. Hence, obtain its unit.
Answer:
Specific heat of a substance,
c = \(\frac{Q}{m\left(T_{\mathrm{f}}-T_{\mathrm{i}}\right)}\), where m is the mass of the substance and Q is the amount of heat supplied to the substance to increase its temperature from Ti to Tf.

The SI unit of heat is the joule (J), that of mass is kg and that of temperature is kelvin (K).
∴ The SI unit of specific heat = \(\frac{\mathrm{J}}{(\mathrm{kg} \cdot \mathrm{K})}\)
[Note: Specific heat is also expressed in J/(kg°C) and cal/(g°C).]

Question 20.
The specific heat of aluminium is 0.21 cal/(g°C). What do you understand by this statement?
Answer:
The amount of heat required to raise the temperature of 1g of aluminium through 1 °C is 0.21 cal.

Question 21.
The specific heat of gold is 0.03 cal/(g°C). Express it in J/(kg°C).
Answer:
1 cal = 4.18 joules (J)
1 gram = 10^-3 kg
∴ 1 cal/(g°C) = 4.18 J/(10-3 kg°C)
= 4180 J/(kg°C)
∴ 0.03 cal/(g°C) = 0.03 × 4180 J/(kg°C)
= 125.4 J/(kg °C)

Question 22.
Arrange the following materials in increasing order of specific heat: aluminium, gold, iron, water.
Answer:
Gold, iron, aluminium, water.

Use your brain power!

Question 1.
Why does your mother put folded cloth strips soaked in cold water on your forehead when you have high fever?
Answer:
To remove heat quickly from our body and thereby lower the temperature of the body (as water has high specific heat).

Question 2.
Why is the calorimeter made of copper?
Answer:
Copper is a good conductor of heat and has low specific heat. Also copper is durable and not highly reactive.

Question 23.
How will you determine the specific heat of a metal using a calorimeter?
OR
Describe the experiment to determine the specific heat of iron using an iron ball, calorimeter and water.
Answer:
1. Find the mass (m_i) of the iron ball.
2. Find the total mass (m_c) of the calorimeter (metal container) and the stirrer.

3. Fill the calorimeter to two-thirds of its capacity with water and find its mass (m’_c) along with the stirrer. Hence, find the mass (m_w) of the water in the calorimeter (m_w = m’_c – m_c).
4. Keep the calorimeter in the wooden box and note the temperature (T₁) of the water in the calorimeter with the thermometer.

5. Suspend the iron ball in water in a beaker. Heat the beaker so that the water starts boiling. Note the temperature (T₂) of the boiling water.
6. Transfer the iron ball quickly to the calorimeter and cover the calorimeter with the lid immediately.

7. Stir the water in the calorimeter gently and continuously for uniformity of temperature and note the maximum temperature (T₃) attained by the mixture.

8. Find the specific heat capacity of iron using the following formula:
heat lost by the iron ball = heat gained by the calorimeter, stirrer and water
[assuming that there is no exchange of heat between the system (calorimeter, stirrer, water and iron ball) and the surroundings].

where cc = specific heat of the material of the calorimeter and stirrer and c_w = specific heat of water.
Hence, the specific heat of iron (c_i) can be determined when other quantities are known.

Question 24.
Why is a calorimeter used in the study of the exchange of heat between a solid and liquid or between two liquids?
Answer:
When a hot body is kept in contact with a cold one, there is an exchange of heat between the two. Hence, the temperature of the hot body decreases while that of the cold body increases till both the bodies attain the same temperature. During this process, if there is no exchange of heat between the surrounding and the bodies, the heat lost by the hot body is equal to the heat gained by the cold body.

As a calorimeter ensures that there is hardly any exchange of heat between the contents of the calorimeter and the surroundings, the calorimeter is used in the study of the exchange of heat between a solid and liquid or between two liquids.

Question 25.
Explain why the inside and outside of a calorimeter are polished.
Answer:

1. A calorimeter is used for the measurement of heat. Hence, it is essential to minimize the exchange of heat between the vessel and the surroundings.
2. A polished surface is a good reflector of heat. Hence, by polishing the inside and outside of a calorimeter, the loss or gain of heat due to radiation is reduced to a considerable extent.

Question 26.
Explain with the help of a formula the coefficient of linear expansion of a solid.
Answer:
Suppose a rod of length l₁ at temperature T₁ is heated to temperature T₂ such that ΔT = T₂ – T₁ is very small. Let l₂ be the length of the rod at temperature T₂.
Experimentally, it is found that the increase in the length of the rod (linear expension), l₂ – l₁, is proportional to l₁ and ΔT. Therefore, (l₂ – l₁) α, l₁ΔT
∴ l₂ – l₁ = λl₁ ΔT, where X is the constant of proportionality, called the coefficient of linear expansion of the solid.
λ = \(\frac{l_{2}-l_{1}}{l_{1} \Delta T}\) It is expressed in per °C.
We have l₂ – l₁ + λΔT = l₁ (1 + λΔT).

Question 27.
Define coefficient off linear explansion of a solid. Write the formula for it and obtain its unit.
Answer:
Coefficient of linear expansion of a solid is defined as the increase in the length of a rod of the solid per unit initial length per unit rise in its temperature.
Coefficient of linear expansion of a solid,
λ = \(\frac{l_{2}-l_{1}}{l_{1} \Delta T}\), where l₁ and l₂ are respectively the initial and final length of the rod of the solid and ΔT is the rise in its temperature.
Unit of λ = \(\frac{\text { unit of length }}{\text { unit of length } \times \text { unit of temperature }}\)

Question 28.
The coefficient of linear expansion of silver is 18 ×10^-6 per °C. What do you understand by this statement?
Answer:
If the temperature of a silver rod of length lm is increased by 1 °C, the length of the rod increases by 18 × 10^-6 m.

Question 29.
Explain with the help of a formula the coefficient of areal expansion of a solid.
Answer:
Suppose a sheet of a solid with surface area A₁ at temperature T₁ is heated to temperature T₂ such that ΔT = T₂ – T₁ is very small. Let A₂ be the surface area of the sheet at temperature T₂. Experimentally, it is found that the increase in the surface area of the sheet (areal expansion), A₂ – A₁, is proportional to A₁ and ΔT. Therefore,
(A₂ – A₁)α A₁ ΔT
∴ A₂ – A₁ = σ Al₁ΔT, where a is the constant of proportionality, called the coefficient of areal expansion of the solid.
σ = \(\frac{A_{2}-A_{1}}{A_{1} \Delta T}\). It is expressed in per °C.
We have A₂ = A₁ + σA₁ΔT = A₁ (1 + σΔT).
σ is the increase in the area of a solid per unit original area per unit rise in its temperature.
[Note: Consider a thin square metal plate of length l. Area of one face of the plate = A = l₂. Suppose the plate is heated so that the rise in its temperature is ΔT (assumed to be very small). Then in the usual notation, Δl = l λΔT and ΔA =
AσΔT = l² σΔT. Also, ΔA = (l + Δl)² – l² = l² + 2l.Δl + Δl² – l2 = 2l.Δl + Δl² . As Δl² << 2l.Δl, we can write ΔA = 2l.Δl(approximately)
∴ ΔA = 2l(l λΔT) = 2l²λΔT but ΔA = l²σΔT
∴ σ = 2.λ]

Question 30.
Explain with the help of a formula the volumetric expansion coefficient of a solid.
Answer:
Suppose a solid with volume V₁ at temperature T₁ is heated to temperature T₂ such that T₁ = T₂ – T₁ is very small. Let V₂ be the volume of the solid at temperature T₂. Experimentally, it is found that the increase
in the volume of the solid (volumetric expansion), V₂ – V₁, is proportional to V₁ and ΔT. Therefore, (V₂ – V₁)α V₁ΔT.
∴ V₂ – V₁ = βV₁ΔT, where β is the constant of proportionality, called the volumetric expansion coefficient of the solid.
β = \(\frac{V_{2}-V_{1}}{V_{1} \Delta T}\) It is expressed in per °C.
We have V₂ = V₁ + βV₁ ΔT = V₁ (1 + βΔT).
is the increase in the volume of a solid per unit original volume per unit rise in its temperature.
[Note: It can be shown that β = \(\frac{3}{2}\) σ 3λ.]

Question 31.
Obtain an expression for the variation of the density of a solid with temperature.
Answer:

As the temperature increases, density decreases.

Use your brain power!

Question 1.
Which use of the expansion of liquids in daily life do you know?
Answer:
Use of a thermometer. The effect of heat on water is somewhat different from that for other liquids. This is called anomalous behaviour of water. We are going to learn about it in higher standard.

Can you recall?

Expansion of gases:

A gas does not even have a fixed volume. Gas expands on heating but if the gas is kept in a closed box, its volume cannot increase but its pressure increases. This is shown in Fig. Observe Fig. and find out answers to the questions.

Question 1.
Using the formula density = mass/volume, explain what will be the effect of heat on the gas kept in a closed bottle.
Answer:
The density of the gas will remain the same as there is no change on the mass and volume of the gas.

Question 2.
If the bottle is not closed but has a movable piston attached to its open end (see the figure), what will be the effect of heating the gas in the bottle?
Answer:
The piston will move upwards as the gas expands.
Therefore, the expansion of a gas is measured by keeping its pressure constant.

Use your brain power!

Question 1.
The density of a gas decreases on heating. Which of the pictures in Fig. makes use of this?
Answer:
Students should be able to answer this question.

Write short notes on the following:

Question 1.
The Celsius temperature scale:
Answer:
In this case, the temperature at which pure ice melts at normal atmospheric pressure is taken as zero degree (0°C) and the temperature at which pure water boils at normal atmospheric pressure is taken as hundred degree (100 °C). The interval between them is divided into loo equal parts. Each part corresponds to a temperature difference of 1 °C.

Question 2.
The Fahrenheit temperature scale:
Answer:
In this case, the normal melting point of pure ice is taken as 32 °F and the normal boiling point of pure water is taken as 212 °F. The interval between these two points is divided into 180 equal parts. Each part corresponds to a temperature difference of 1°F. If C is the temperature of a body on the Celsius scale and F is the corresponding temperature on the Fahrenheit scale, the two are related by
C = \(\frac{5}{9}\) (F – 32) or F = \(\frac{9}{5}\) C + 32.

Question 3.
The Kelvin temperature scale:
Answer:
In this case, the melting point of pure ice at normal atmospheric pressure is taken as 273.15 kelvin (273.15 K) and the boiling point of pure water at normal f atmospheric pressure is taken as 373.15 I kelvin (373.15 K). The lowest possible temperature (called the absolute zero) on this scale corresponds to -273.15 °C.

Give scientific reasons:

Question 1.
We heat the neck of a glass bottle in order to remove the firmly fitted stopper.
Answer:
When we heat the neck of the glass bottle, it expands. Due to this, the stopper becomes loose and can be removed with ease.

Question 2.
A clinical thermometer has to be jerked before re-use.
Answer:
The constriction above the bulb of the clinical thermometer prevents the mercury thread once risen from falling down to the bulb. Hence, in order to force the mercury thread back into the bulb, the 1 clinical thermometer has to be jerked before re-use.

Question 3.
Instead of the mercury thermometer, alcohol thermometer is used for measurement of very low temperature.
Answer:
Mercury freezes at – 39 °C and turns to a solid. Hence, the mercury thermometer cannot be used to measure temperature below -39°C. The freezing point of alcohol is -117°C. Hence, the alcohol thermometer is used for i measurement of very low temperature.

Solve the following examples:

Question 1.
The normal armpit temperature in humans is 98.6 °F. What is this temperature in (i) degree Celsius (ii) kelvin ?
Solution:
Data: F = 98.6 °F, C = ?, K = ?

(ii) K = C + 273.15
= 37 + 273.15 = 310.15 K.

Question 2.

Find the heat needed to raise the temperature of 2.5 kg of water from 30 °C to 40 °C. Write the answer in calorie as well as joule.
Solution:
Data: m = 2.5 kg = 2500 g,
ΔT = 40 °C-30 °C, Q = ?
Heat needed to raise the temperature of 1 g of water through 1°C is 1 calorie.
∴ Q = 2500 × 10 = 25000 calories
Now, 1 calorie = 4.18 joules
∴ Q = 25000 × 4.18 joules = 104500 joules
Heat needed, Q = 25000 calories = 104500 joules.

Question 3.
If the temperature of water rises by 5 °C when 500 cal of heat is supplied to it, what is the mass of water?
Solution:
Mass of water = \(\frac{500}{5}\) = 100 g.

Question 4.
How much heat is required to raise the temperature of 500 g of mercury from 20 °C to 100 °C? [Specific heat of mercury = 0.033 kcal/(kg °C)]
Solution:
Data: m = 500 g = 0.5 kg,
T₁ = 20 °C,
T₂ = 100 °C, c = 0.033 kcal/(kg . °C), Q = ?
Q = mc (T₂ – T₁)
= 0.5 kg × 0.033 kcal/(kg . °C) × (100 °C – 20 °C)
= 0.5 × 0.033 × 80 kcal
= 0.033 × 40 kcal
∴ Q = 1.32 kcal
Heat required = 1.32 kcal.
[Note: 1kcal/(kg-°C) = 1 cal/(g.°C)]

Question 5.
A certain mass of water at 84 °C is poured into an equal mass of water at 24 °C. What will be the resulting temperature of the mixture ?
Solution:
Data: mx = m2 = m (say),
T₁ = 84 °C, T₂ = 24 °C, T = ?
Heat lost by the hot water = heat gained by the cold water

Resulting temperature of the mixture = 54 °C.

Question 6.
A bucket contains 8 kg of water at 20 °C. When 4 kg of hot water is mixed with it, the temperature of the mixture becomes 40 °C. Calculate the temperature of the hot water. (Ignore the heat absorbed by the bucket.)
Solution:
Data: m₁ = 8 kg, T₁ = 20 °C, m₂ = 4 kg, T = 40 °C, T₂= ?
Heat lost by the hot water = heat gained by the cold water (ignoring the heat absorbed by the bucket)
∴ m₂c (T₂ – T) = m₁c (T – T₁)
∴ 4 kg × c × (T₂ – 40°C)
= 8 kg × c × (40°C – 20°C)
∴ T₂ – 40°C = 2 × 20°C = 40°C
∴ T₂ = 40 °C + 40 °C = 80 °C
Temperature of the hot water = 80 °C.

Question 7.
A blacksmith plunges a 2 kg horseshoe at 400 °C into 1 kg of water at 20 °C. Find the maximum temperature of the water. [Specific heat of iron = 0.11 kcal/(kg-°C)]
Solution:
Data: mx = 2 kg,
c₁ = 0.11 kcal/(kg.°C), T₂ = 400 °C, m₂ = 1 kg,
c₂ = 1 kcal/(kg.°C), T₂ = 20 °C, T = ?
Heat lost by the horseshoe = heat gained by the water
∴ m₁c₁ (T₁ – T) = m₂c₂(T – T₂)
∴ 2 kg × 0.11 kcal/(kg.°C) × (400 °C – T)
= 1 kg × 1 kcal/(kg.°C) × (T – 20 °C)
∴ 0.22 × (400 °C – T) = T – 20 °C
∴ 1.22 T= 108 °C
∴ T = \(\frac{108}{1.22}\)°C = 88.52 °C
Maximum temperature of the water = 88.52 °C.

Question 8.
A copper sphere of mass 500 g is heated to 100 °C and then introduced into a copper calorimeter containing 100 g of water at 20 °C. Find the maximum temperature of the mixture, if the mass of the calorimeter is 100 g and the specific heat of the calorimeter is 0.1 cal/(g.°C).
Solution:
Data: m = 500 g, c = 0.1 cal/(g.°C), T’= 100 °C, m₁ = 100 g, c₁ = 1 cal/(g.°C), T₁ = 20°C, m₂ = 100 g, c₂ = 0.1 cal/(g.°C), T₂ = 20 °C, T= ?
Heat lost by the sphere = heat gained by the water and the calorimeter.
∴ mc (T’ – T) = m₁c₁ (T – T₁) + m₂c₂ (T – T₂)
∴ 500 g × o.l cal/(g.°C) × (100 °C – T)
= 100 g × 1 cal/(g.°C) × (T – 20 °C) + 100 g × 0.1 cal/(g.°C) × (T – 20 °C)
∴ 50 (100 °C – T) = 100 × (T – 20 °C) + 10 × (T – 20 °C)
∴ 50 (100 °C – T) = 110 × (T – 20 °C)
∴ 500 °C – 5T = 11T – 220 °C
∴ 16T = 720 °C
∴ T = \(\frac{720^{\circ} \mathrm{C}}{16}\) = 45 °C
Maximum temperature of the mixture = 45 °C.

Question 9.
A metal rod 1.8 m long, increases ( in length by 1.4 mm, when heated from 0 °C to 50 °C. Find the coefficient of linear expansion of the metal.
Solution:
Data: l₁ = 1.8 m, l₂ – l₁ = 1.4 mm = 1.4 × 10^-3 m.
T₁ = 0 °C, T₂ = 50 °C.
l₂ – l₁ = l₁ λ (T₂ – T₁)
∴ The coefficient of linear expansion of the metal is

Question 10.
A thin metal disc of surface area 500 cm2 at 0 °C is heated to 40 °C. Find the increase in the surface area of the disc. (σ = 4 × 10^-5 °C ^-1)
Solution:
Data: A₁ = 500 cm², T₁ = 0 °C,
T₂ = 40 °C, σ = 4 × 10^-5 °C^-1, A₂ – A₁ = ?
The increase in the surface area of the disc is
A₂ – A₁ = A₁σ(T₂ – T₁)
= (500 cm²) (4 × 10^-5 °C^-1) (40 °C – 0 °C)
= 500 × 4 × 10^-5 × 40 = 0.8 cm².

Question 11.
The surface area of a metal plate is 2.4 × 10^-2m² at 20 °C. When the plate is heated to 185 °C, its area increases by 0.8 cm². Find the coefficient of areal expansion of the metal.
Solution:
Data: A₁ = 2.4 × 10^-2 m²,
T₁ = 20 °C, T₂ = 185 °C, ΔA = 0.8 cm² = 0.8 × 10^-4 m², σ = ?
ΔA = A₂ – A₁ = A₁ σ(T₂ – T₁)
∴ The coefficient of areal expansion of the metal is

Question 12.
A lead bullet has a volume of 25 cm³ at 0 °C, and 25.21 cm³ at 90 °C. Find the volumetric expansion coefficient of lead.
Solution:
Data: V₁ = 25 cm³, T₁ = 0 °C,
V₂ = 25.21 cm³, T₂ = 90 °C
T₂ – T₁ = 90 °C – 0 °C = 90 °C β = ?

The volumetric expansion coefficient of lead is 9.333 × 10^-5 °C^-1.

Example Questions for practice:

Question 1.
The temperature of a body is 30 °C. Express it in (i) degree Fahrenheit (ii) kelvin.
Answer:
86 °F, 303.15 K

Question 2.
The temperature of a body is 283.15 K. Express it in °C and °F.
Answer:
10 °C, 50 °F

Question 3.
The temperature of a body is 68 °F. Express it in °C and K.
Answer:
20 °C, 293.15 K

Question 4.
Find the heat needed to raise the temperature of 5 kg of water from 20 °C to 25 °C. Write the answer in calorie as well as joule.
Answer:
25 × 10³ cal, 1.045 × 10⁵ J

Question 5.
When a substance having mass 2 kg absorbs 2000 cal of heat, its temperature increases by 10 °C. Find the specific heat of the substance.
Answer:
0.1 cal/(g.°C)

Question 6.
Find the heat needed to raise the temperature of 100 g of a metal through 10 °C if the specific heat of the metal is 0.1 cal/g. °C.
Answer:
100 cal

Question 7.
If water of mass 80 g and temperature 40 °C is mixed with water of mass 20 g and temperature 25 °C, what will be the maximum temperature of the mixture?
Answer:
37 °C

Question 8.
A metal rod 2.5 m long, increases in length by 1.25 mm when it is heated from 10 °C to 60 °C. Find the coefficient of linear expansion of the metal.
Answer:
1 × 10^-5 °C^-1

Question 9.
The surface area of a metal plate is 2 × 10^-2 m² at 10 °C. When the plate is heated to 60 °C, its area increases by 0.2 m². Find the coefficient of areal expansion of the metal.
Answer:
2 × 10^-5 °C^-1

Question 10.
A metal ball has volume 50 cm3 at 0 °C and 50.4 cm3 at 100 °C. Find the volumetric expansion coefficient of the metal.
Answer:
8 × 10^-5 °C^-1

Project:

Ref. Project. Useful information:
A bimetallic strip: A bimetallic strip consists of two strips of equal lengths but of different metals rivetted together. At room temperature the strip is straight.

Question 1.
The principle on which a bimetallic strip works:
Answer:
When two different metal strips of the same length at a given temperature are heated to the same higher temperature, they expand in different proportion.
A bimetallic strip of brass and iron is straight at room temperature. The expansion of brass is nearly 1.5 times that of iron. Hence, when this bimetallic strip is heated, it bends, making the iron side concave.

Question 2.
How a bimetallic strip is used in fire alarm:
Answer:
A bimetallic strip of brass and iron is

connected to a battery and an electric bell as shown in the diagram. One terminal of the bell is connected to a screw which is at a very small distance from the iron side of the strip. In case, there is an accidental fire, the bimetallic strip bends towards iron and touches the screw. Thus, the circuit is completed and the bell rings, thereby warning the people of the accidental fire.

Balbharati Maharashtra State Board 8th Std Science Textbook Solutions

• Human Body and Organ System Class 8 Science Textbook Solutions
• Introduction to Acid and Base Class 8 Science Textbook Solutions
• Chemical Change and Chemical Bond Class 8 Science Textbook Solutions
• Measurement and Effects of Heat Class 8 Science Textbook Solutions
• Sound Class 8 Science Textbook Solutions
• Reflection of Light Class 8 Science Textbook Solutions
• Man-made Materials Class 8 Science Textbook Solutions
• Ecosystems Class 8 Science Textbook Solutions
• Life Cycle of Stars Class 8 Science Textbook Solutions