Category: Class 8

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

Maharashtra State Board Class 8 Science Solutions Chapter 5 Inside the Atom

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:

Thomson’s atomic model	Rutherford’s atomic model
1. According to Thomson’s atomic model, the negatively charged electrons are embedded in a gel of positive charge.	1. According to Rutherford’s atomic model the negatively charged electrons revolve around the nucleus.
2. Atom is homogenous sphere of positive charge.	2. The positive charge is in the nucleus of the atom.

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.

Column I	Column II
1. Proton	a. Negatively charged
2. Electron	b. Neutral
3.  Neutron	c. Positively charged

Answer:

Column I	Column II
1. Proton	c. Positively charged
2. Electron	a. Negatively charged
3. Neutron	b. Neutral

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.

Column I	Column II
1. Thomson	a. Well defined orbits
2. Rutherford	b. Neutron
3. Chadwick	c. Scattering experiment
4. Bohr	d. Electron

Answer:

Column I	Column II
1. Thomson	d. Electron
2. Rutherford	c. Scattering experiment
3. Chadwick	b. Neutron
4. Bohr	a. Well defined orbits

Question 2.

Column I	Column II
1. Atom	a. Treatment of goitre
2. Isotopes of iodine	b. Protons + Neutrons
3. Atomic mass number	c. Different number of neutrons
4. Isotopes	d. Electrically neutral

Answer:

Column I	Column II
1. Atom	d. Electrically neutral
2. Isotopes of iodine	a. Treatment of goitre
3. Atomic mass number	b. Protons + Neutrons
4. Isotopes	c. Different number of neutrons

Question 3.

Column I	Column II
1. Alpha particles	a. Inert element
2. Uranium-235	b. Negatively charged particles
3. Helium	c.   Positively charged particles
4. Isotopes	d.   Krypton – 92, Barium 141
	e.   U-233, Th-232
	f.    12C, 13C, 14C

Answer:

Column I	Column II
1. Alpha particles	c. Positively charged particles
2. Uranium-235	d. Krypton – 92, Barium 141
3. Helium	a. Inert element
4. Isotopes	f.    12C, 13C, 14C

Distinguish between the following:

Question 1.
Proton and Neutron:
Answer:

Proton	Neutron
1. The proton is positively charged particle	1. The neutron does not have any charge.
2. In an atom, the number of protons is always equal to the number of electrons.	2. In general, in an atom, the number of neutrons is not equal to the number of electrons.

Question 2.
Neutron and Electron:
Answer:

Neutron	Electron
1. The neutron is an electrically neutral particle.	1. The electron is a negatively charged particle.
2. Neutrons are present in the nucleus of an atom.	2. Electrons revolve around the nucleus of the atom in specific orbits.

Question 3.
Proton and Electron:
Answer:

Proton	Electron
1. The proton is a positively charged particle	1. The electron is a negatively charged particle.
2 Protons are present in the nucleus of an atom.	2. Electrons revolve around the nucleus of the atom in specific orbits.

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

Atomic number	Atomic mass number
1. The number of electrons or protons in an atom is called the atomic number.	1. The sum of the number of protons and neutrons in the nucleus of an atom is called the atomic mass number.
2 All the isotopes of an element have the same atomic number.	2. Different isotopes of the same element have different mass numbers.
3. The atomic number is represented by the letter Z.	3. The atomic mass number is represented by the letter A.

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:

Isotopes	Proton number	Neutron number
\({ }_{1}^{1} \mathrm{H}\)	1	–
\({ }_{1}^{2} \mathrm{H}\)	1	1
\({ }_{17}^{35} \mathrm{Cl}\)	1	2
\({ }_{17}^{35} \mathrm{Cl}\)	17	18
\({ }_{17}^{37} \mathrm{Cl}\)	17	20

 

Balbharti Maharashtra State Board Class 8 Geography Solutions Chapter 7 Population Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Geography Solutions Chapter 7 Population

Class 8 Geography Chapter 7 Population Textbook Questions and Answers

1. Complete the following sentences:

Question A.
If the birth rate is greater than the death rate then the population …………. .
(i) decreases
(ii) increases
(iii) remains constant
(iv) becomes surplus
Answer:
(ii) increases

Question B.
People of …………… age group are included in the productive population.
(i) 0 to 14
(ii) 14 to 60
(iii) 15 to 60
(iv) 16 to 59
Answer:
(iv) 16 to 59

Question C.
The spread of modern technology in society is mostly dependent on …………….. .
(i) sex ratio
(ii) birth rate
(iii) literacy
(iv) migration
Answer:
(iv) migration

2. Examine the following statements and correct the incorrect ones:

Question a.
The population density of a region can be understood from its area.
Answer:
Incorrect.
Correct sentence: The population density of a region can be understood from its area and the total volume of population living in it.

Question b.
The quality of population is determined on the basis of literacy.
Answer:
Correct.

Question c.
There is an adverse impact on manpower in the regions of out migration.
Answer:
Correct.

Question d.
Greater economic prosperity indicates the development of region.
Answer:
Incorrect.
Correct sentence: Greater economic prosperity as well as higher standards of living, higher quality of life, availability of opportunities, freedom, etc, indicate the development of region.

Question e.
Developing countries have an HDl of 1.
Answer:
Incorrect.
Correct sentence: Developing countries have and HDI of 0.50 to 0.60.

3. Answer in brief.

Question a.
What are the aspects considered in the structure of population?
Answer:
The following are the aspects considered in the structure of the population:

1. Sex ratio/structure: Sex ratio/structure is a structure that considers the sub division of population on the basis of gender.
2. Age structure: Age structure is a structure that considers the sub division of population as per age groups.
3. Occupational structure: Occupational structure is a structure that considers sub division of population on the basis of dependency and workability.
4. Rural – urban structure: Rural – Urban structure is a structure that considers sub division of population on the basis of area of residence.
5. Literacy structure: Literacy structure is a structure that considers sub division of population on the basis of capability of reading and writing.

Question b.
Prepare a list of advantageous and disadvantageous factors, affecting population distribution.
Answer:
A list of advantageous factors affecting population distribution is as follows:

1. Availability of sufficient sunlight, clean air and water.
2. Region with low altitude
3. Moderate rainfall and temperature
4. Fertile soil
5. Deposits of minerals
6. Industrialisation
7. Urbanisation
8. Availability of transportation facilities
9. Availability of market
10. Political stability
11. International peace
12. Favourable government policies
13. Favourable social customs and traditions.

A list of disadvantageous factors affecting population distribution is as follows:

1. Shortage of sufficient sunlight, clean air and water.
2. Region with high altitude
3. Extremely less or more rainfall and temperature
4. Infertile soil
5. Scarcity of minerals
6. Low industrialisation
7. Lack of urbanisation
8. Non-availability of transportation facilities
9. Non-availability of market
10. Political instability
11. International disputes
12. Unfavourable government policies
13. Evil social customs and traditions.

Question c.
What are the problems in areas of high population densities?
Answer:
The ratio of the population of a country to its area is population density. While discussing population distribution, density of population is also considered. The density is calculated, as per the formula given below.
Density of population = Population of a region/Area of a region.

The problems in areas of high population densities are as follows:
1. Pollution – Pollution is one of the major reasons which people face due to high population density. Due to an increase in land degradation by making houses and flats, land pollution will be caused, water will be contaminated by a huge number of people, resulting in water pollution and huge number of vehicles will cause air pollution.

2. Overcrowded – The areas with high population density become overcrowded, which bring chaos and lack of peace in the society.
3. Lack of open space – High population density makes it difficult to get a free open space.

Question d.
What arc the problems in area of low population densities?
Answer:
The development of a country depends upon its size of population. A lower population is somehow manageable and resources can be distributed equally. But, sometimes the low population leads to lower demands of goods and services and lower tax revenues for the government to provide goods and services.

4. Give geographical reasons:

Question a.
Population is an important resource.
Answer:

1. The economic and cultural development of any country depends upon the volume and the quality of population.
2. If a country has a high volume and less quality of population, it has slow economic growth and development.
3. If a country has optimum population with high quality of population, it has fast economic growth and development. Thus, population is an important resource.

Question b.
Productive population is an important group.
Answer:

1. People belonging to age group of 16 to 59 age are considered as productive. Therefore this population is called productive population.
2. People below 16 years of age and above 60 years of age are considered as dependent or non-working population.
3. Productive population/people are involved in services or businesses. Therefore they play very important role in economic
4. If country has more proportion of productive population and youth, it develops rapidly. Thus, productive population is an important group.

Question c.
The study of age structure is important.
Answer:

1. The study of age structure helps to know the percentage of children, adolescents, youth, middle aged, and old aged in population.

2. The study of age structure helps to know the proportion of productive people (Working people between 16 years to 59 years of age) and unproductive people (Non working people below 16 years of age and above 60 years of age).

3. The study of age structure helps government in planning various economic, social, educational, medical, etc. schemes for the overall development of country.

4. The study of age structure helps to know the speed of economic growth. Thus, the study of age structure is important.

Question d.
Literacy is directly related to development.
Answer:

1. The country with high literacy rate, develops rapidly in economic, social and cultural aspects.
2. The country with low literacy rate, faces many obstacles in its economic, social and cultural growth and development.
3. Literacy rate is related to quality of life, the opportunities available and freedom. Thus, literacy is directly related to development.

Question e.
The real progress of a country is understood with the help of the Human Development Index.
Answer:
1. Human Development Index is calculated by taking into account the values of economic, health and education parameters.

2. Thus, Human Development Index is calculated on the basis of Gross National Product, life expectancy and literacy rate.

3. Human Development Index indicates the standard of living, economic and social welfare, quality of life, opportunities available and freedom. Therefore, the real progress of a country is understood with the help of the Human Development Index.

5. Write notes.

Question a.
Sex ratio.
Answer:
1. The number of females per thousand males is called sex ratio.

2. The sex ratio is calculated with the help of the following formula :

3. If the number of females per thousand males is less, the sex ratio is considered to be low. On the other hand, if the number of females per thousand males is more, the sex ratio is considered to be high.

4. According to Census 2011, the sex ratio was highest (1084) in the state of Kerala. According to Census 2011, the sex ratio was 929 in the state of Maharashtra.

5. Out-migration of males leads to high sex ratio in a region from where males have out-migrated. Less female birth rate leads to low sex ratio.

Question b.
Age structure.
Answer:

1. Sub division of population as per age groups is known as age structure.
2. Age structure is helpful in knowing the proportion of children, adolescents, young, middle aged and old people in population.
3. It is also helpful in knowing proportion of active population (Population between the ages 16 and 59) and dependent population (Population below 16 years of age and above 60 years of age).
4. Age structure is helpful to the government in framing various policies.

Question c.
Literacy.
Answer:
1. Population above the age of seven can be sub divided on the basis of capability of reading and writing.

2. People above the age of seven and are unable to read and write are considered illiterate. On the other hand, people above the age of seven and are able to read and write are considered literate.

3. High literacy rate is an indicator of social and economic development of society. On the other hand, high illiteracy rate leads to slow economic, social and cultural development of society.

4. Literacy rate is related to quality of life, the opportunities available and freedom. Thus, it is directly related to development.

Activity:

Question a.
Survey 5 families in your neighbourhood on the basis of the following points and make a presentation.
(a) Sex
(b) Age groups
(c) Education
(d) Occupation

Class 8 Geography Chapter 7 Population Additional Important Questions and Answers

Fill in the correct word and complete the sentences:

Question A.
……………… state of India has the highest sex ratio.
(i) Maharashtra
(i) Kerala
(c) Punjab
(d) Haryana
Answer:
(b) Kerala

Question B.
………………. district of Maharashtra has low density of population.
(a) Mumbai City
(b) Mumbai Suburb
(c) Thane
(d) Osmanabad
Answer:
(d) Osmanabad

Examine the following statements and correct the incorrect ones:

Question a.
The state of Maharashtra has a balanced population.
Answer:
Incorrect.
Correct sentence: The state of Maharashtra has imbalanced population.

Question b.
The areas with plenty of natural resources normally have more volume of population.
Answer:
Correct.

Question c.
The region with more proportion of youth in population has a rapid speed of development.
Answer:
Correct.

Question d.
Most of people in rural areas are engaged in tertiary activities.
Answer:
Incorrect.
Correct sentence: Most of people in rural areas are engaged in primary activities.

Question e.
Human Development Index is published by World Health Organisation.
Answer:
Incorrect.
Correct sentence: Human Development Index is published by United National Development Programme.

Question f.
Density of population is found to be more in the state of Goa.
Answer:
Correct.

Question g.
The state of Rajasthan is densely populated.
Answer:
Incorrect.
Correct sentence: The state of Rajasthan is sparsely populated.

Answer the following questions in one sentence each:

Question a.
What is birth rate?
Answer:
Birth rate is the number of live births per one thousand people in a year.

Question b.
What is death rate?
Answer:
Death rate is the number of deaths per one thousand people in a year.

Question c.
What is life expectancy?
Answer:
Life expectancy is the expected average life span of an individual at the time j of his/her birth.

Question d.
What is meant by in-migration?
Answer:
Migration of people in a particular region from outside regions is known as in-migration.

Question e.
What is meant by out-migration?
Answer:
Migration of people from a particular region to outside regions is known as out-migration.

Question f.
What is meant by sex ratio?
Answer:
The total number of females per thousand males is known as sex ratio.

Question g.
In which types of occupations are people in urban areas involved?
Answer:
People in urban areas are involved in secondary and tertiary occupations.

Question h.
Who put forth the concept of Human Development Index?
Answer:
Mahbub Ul Haq and Amartya Sen put forth the concept of Human Development Index.

Answer the following questions in brief:

Question a.
Explain the various types of migration.
Answer:
The various types of migration are as follows:

1. In-migration: In-migration is migration of people in a particular region from outside regions.
2. Out-migration: Out-migration is migration of people from a particular region to outside regions.
3. Short term mfgration: Short term migration is migration of people on a i temporary basis. For example, migration due to tourism or natural disaster or education is a short term migration.
4. Long term migration: Long term migration is migration of people on a permanent basis. For example, migration due to transfer of service or marriage or war j and partition is a long term migration.

Question b.
Explain the effects of migration.
Answer:
The effects of migration are as follows:

1. Out-migration leads to fall in population of a region from where people have migrated outside. This in turn leads to shortage of manpower in a region from where out-migration has occurred.

2. In-migration leads to increase in population of a region in which people from outside regions have migrated. This in turn, puts a pressure on public amenities and infrastructure of a region in which people have migrated.

3. Migration leads to redistribution of population.
4. Migration also leads to a change in the structure of population in a particular region.

Give geographical reasons:

Question a.
The density of population is found to be high in Mumbai City and Mumbai Suburb district.
Answer:

1. Mumbai is economic capital of India.
2. In Mumbai City and Mumbai Suburb district, industrialisation and urbanisation has taken place on a large scale.
3. Transportation, educational, medical, etc. facilities are available on a large scale in these districts.
4. Many employment opportunities are also available in these districts.

Due to all these favourable factors, many people from other districts of Maharashtra as well as from other states of India have migrated to Mumbai on a permanent basis. Therefore, the density of population is found to be high in Mumbai City and Mumbai Suburb district.

Study the following map/figure/graph and answer the following questions:

Study the Figure is given and answer the following questions:

Question a.
Which state has the highest sex\ratio?
Answer:
Kerala state has the highest sex j ratio.

Question b.
Which state has the lowest sex J ratio?
Answer:
Haryana state has the lowest sex ratio.

Question c.
What changes should take place in Maharashtra, to bring about a balanced > sex ratio and how much change is i necessary?
Answer:
The following changes should take place in Maharashtra to bring about a balanced sex ratio:

1. Sex ratio must get increased by having total control over female infanticide and launching various government schemes for women empowerment, etc.
2. The sex ratio must get increased by 71 i.e. the number of females per thousand males must get increased from 929 to 1000.

Try this: 

Question a.
Prepare bar graphs on the basis of the table given below and write a note. (Discuss in group about the issue of literacy in the country.)?

Answer:
(A) Bar graph:

(B) Note:

1. From the above bar diagram it can be seen that the literacy rate is found to be high in developed countries, moderate in developing countries and low in underdeveloped countries.
2. In 2010, the literacy rate was 72.1°/e in India.
3. In 2010, the literacy rate was 98.1% in Argentina and it was 38.1% in Afghanistan.
4. Literacy rate is directly or indirectly related to quality of life, opportunities available and the freedom.

Can you tell? 

Study Figure is given and answer the following questions:

Question a.
Which are the most densely populated districts?
Answer:
The most densely populated districts are:

1. Mumbai City
2. Mumbai Suburb
3. Thane
4. Pune
5. Kolha5ur, etc.

Question b.
Name the sparsely populated districts with a density of less than 100 per sq. km.
Answer:
The sparsely populated districts with a density of less than 100 sq. km:

1. Gadchiroli
2. Beed
3. Osmanabad, etc.

Question c.
Name two districts with moderate population.
Answer:
District with moderate population:

1. Nashik
2. Nagpur.

Question d.
What is the density of the dark shaded regions?
Answer:
The density of the dark shaded regions is greater than 1000 person per sq. km.

Question e.
Why is the density of population less in Gadchiroli?
Answer:
The density of population is less in Gadchiroli due to dense forests.

Question f.
Have a discussion in the class on the effect of physiography, climate, area under forest, industries, etc. on the density of population.
Answer:
1. Physiography: The density of population is found to be high in plain areas. On the other hand, the density of population is found to be low in mountainous regions.

2. Climate: The density of population is found to be high in the areas with moderate temperature and moderate rainfall. On the other hand, the density of population is found to be low in the areas of extremely low or high temperature and extremely high or low rainfall.

3. Area under forest: The density of population is found to be high in the area where forest cover is limited. On the other hand, the density of population is found to be low in the area under dense forests.

4. Industries: The density of population is found to be high in industrially developed region. The density of population is found to be low in industrially backward: region.

Thought-Provoking Questions:

Can you tell? 

Study the table is given and answer the following questions:

Question a.
Which city has greater number of newly born children?
Answer:
‘B’ City has greater number of newly born children.

Question b.
Which city records greater number of deaths?
Answer:
‘B’ City records greater number of deaths.

Question c.
Looking at the figures of in-migration and out-migration which city has received more migrants?
Answer:
Looking at the figures of in-migration and out-migration, ‘A’ City has received more migrants. .

Question d.
Calculate the population of both the cities in 2017.
Answer:
The population of ‘A’ City in 2017 is 121, 500 and of ‘B’ City in 2017 is 120, 550.

Question e.
After considering all the points, which city has recorded more growth of population in one year?
Answer:
After considering all the points, ‘A’ City has recorded more growth of population in one year. .

Question f.
The total number of births are given. What would be this figure per thousand population? What is the term for this?
Answer:
The total number of births are given. This figure would be 20 per thousand. The term for this is ‘Birth rate’.

Question g.
What would be the number of deaths per thousand population? What is the term used for this?
Answer:
The number of deaths per thousand would be 25. The term used for this is ‘Death rate’.

Complete the following table:
(Note: The answer is given directly.)

Question a.

Answer:

State	Population (2011)	Area (Sq. Km)	Density
1. Uttar Pradesh	19,98,12,341	2,40,926	829.35
2. Maharashtra	11,23,74,333	3,07,713	356.19
3. Tamil Nadu	7,26,26,809	1,30,058	558.41
4. Rajasthan	68,54,837	3,42,239	20.02
5. Manipur	27,21,756	22,327	121.90
6. Goa	14,58,545	3,702	393.98

Think about it:

Question a.
Even though area wise Rajasthan is a large state, the population is less. Which geographical factors may be responsible for this?
Answer:
The amount of rainfall is comparatively less in the state of Rajasthan. The Thar desert is located in the western part of the state of Rajasthan. Therefore, even though area wise Rajasthan is a large state, the population is less.

Can you tell? 

Question a.
Classify Male, Adolescent, Illiterate, Children, Unemployed, Infants, Literate, Rural, Working population, Urban, Female, Old, Young, Dependent population and Adult into the following categories:

1. Sex
2. Age
3. Rural
4. Urban
5. Literacy
6. Productive population.

Answer:

1. Sex: Male, Female
2. Age: Adolescent, Children, Infants, Old, Young, Adult
3. Rural: Rural
4. Urban: Urban
5. Literacy: Illiterate, Literate
6. Productive population: Unemployed, Working population, Dependent population.

Can you tell? 

Study the figure and answer the following questions:

Question a.
What do you think are the reasons for the changing land use pattern of Mondha village?
Answer:
Urbanisation and rise in population are the reasons for the changing land use pattern of Mondha village.

Question b.
What kind of changes have taken place?
Answer:
In Mondha village, the agricultural land use has decreased and the non-agricultural land use (i.e. commercial land use, residential land use) has increased.

Question c.
Due to this change in land use, do you think there has been a change in population? If yes, what is the change and why?
Answer:
Due to this change in land use, there has been a change in population. The population of Mondha has increased due to the in-migration.

Can you tell?

Study the table showing percentage of immigrant population of various countries given on page 46 and answer the following questions:

Question a.
Which countries have less than 10% migrant population?
Answer:
Afghanistan, Brazil, Bangladesh, India and Great Britain have less than 10% migrant population.

Question b.
Which are the countries with a migrant population of between 10% and 20%?
Answer:
Germany and U.S.A. are the countries with a migrant population of between 10%
and 20%.

Question c.
Which are the countries with a migrant population of more than 20%
Answer:
Kuwait, Hong Kong, Oman and Saudi Arabia are the countries with a migrant population of more than 20%.

Question d.
Find the reasons behind the migrant population of more than 20%.
Answer:
The reasons behind the migrant population of more than 20% are:

1. Huge stock of mineral oil and other natural resources
2. Availability of employment opportunities
3. Great demand for labour in these countries.

Question c.
Draw pie diagrams for any two countries.
Answer:
1. Kuwait: A pie diagram showing percentage of immigrant population for Kuwait is as follows:

2. Oman: A pie diagram showing percentage of immigrant population for Oman is as follows:

Question d.
Have a discussion on migration and development.
Answer:
1. Out-migration leads to a shortage of manpower/labour supply. This in turn adversely affects the development of the region from where out-migration has occurred.
2. In-migration leads to increase in population of a region in which in-migration has occurred. This too, adversely affects the development of the respective region.
3. The migration up to certain extent increases the mobility of labourer and it boosts the development of a particular region.

Use your brainpower: 

Question a.
In India, 0.52 % of the population are migrants. What is the actual number of people who have migrated to India?
Answer:
According to Census 2011, the population of India was nearly 121 crore. In India, 0. 52 % of the population are migrants. Thus, according to Census 2011, the actual number of people who have migrated to India is nearly 629,200.

Try this:

Question a.
Write a note on the Human Development Index. (HDI) of various countries on the basis of the following table:
HDI Rank wise Country Value of HDI Level of Development

Answer:

1. Norway ranks first in the world with respect to Human Development Index (HDI). The value of HDI for Norway is 0.949.
2. The countries like Japan, United Kingdom, Denmark, Switzerland, Germany and Australia have the value of Human Development Index (HDI) more than 0.900. These countries show very high level of development.
3. The countries like Sri Lanka, Brazil and China have the value of Human Development Index (HDI) between 0.700 and 0.800. These countries show high level of development.
4. The countries like India, Bhutan and Pakistan have the value of Human Development Index (HDI) between 0.500 and 0.600. These countries show medium level of development.
5.  The countries like Niger and Central African Republic have value of Human Development Index (HDI) between 0.300 and 0.400. These countries show less development.
6. From the above table it can be seen that Human Development Index (HDI) is an indicator of development.
7. Higher value (around 1) of Human Development Index indicates high level of development and lower value (around 0) of Human Development Index indicates low level of development.

Use your brain power:

Question a.
Discuss and write the advantages and disadvantages of low population or high population with reference to the following factors:
(Note: The answer is given directly.)

Answer:

Headings	Low population	High population
Per capita land availability	Per capita land availability is comparatively more.	Per capita land availability is comparatively less.
Foodgrains	Food grains are available in plenty.	There is shortage of food grains.
Resources	Resources are available in plenty.	There is strain on resources.
Per capita income	Per capita income is comparatively high.	Per capita income is comparatively low.
Basic amenities and facilities	Basic amenities and facilities are available in sufficient quantity.	There is strain on basic amenities and facilities.
Percentage of unproductive consumers	Percentage of unproductive consumers is comparatively low.	Percentage of unproductive consumers is comparatively high.
Planning	Planning is comparatively more effective.	Planning is comparatively less effective.
Employment	More employment opportunities are available.	Less employment opportunities are available.
Urbanisation	The rate of urbanisation may be comparatively low.	The rate of urbanisation may be comparatively high.
Health	The quality of health may be comparatively high.	The quality of health may be comparatively low.
Higher education	The number of highly qualified people may be comparatively more.	The number of highly qualified people may be comparatively low.
Social environment	Social environment may be comparatively supportive and favourable.	Social environment may be comparatively adverse and unfavourable.

Give it a try:

Question a.
Since the past two centuries, the size of family is decreasing. But inspite of this the population of the country is increasing. Find out why is this happening.
Answer:
1. Since the past two centuries, the death rate in India has reduced to a great extent. On the other hand, since the past two centuries, the birth rate in India has reduced negligibly. Therefore, since the past two centuries, the size of family is decreasing. But in spite of this the population of country is increasing.

Use your brain power:

Question a.
As per the population Census of 2011, the population of India is 121 crores. For domestic use, the per capita requirement per day is 50 litres of water. Taking this into account, what would be the total amount of water requirement in India for domestic purpose only.
Answer:

1. As per the Population Census of 2011, the population of India is. 121 crores?
2. For domestic use, the per capita requirement per day is 50 litres of water.
3. Taking this into account, the total amount of water requirement in India for domestic purpose only, will be nearly 6050 crores litre.

Open-Ended Questions:

Question a.
What are the problems in areas of high population distribution?
Answer:
The following are the problems in areas of high population distribution:

1. Increased level of water, air, sound and soil pollution.
2. Traffic jam
3. Shortage of residential areas
4. Increased criminal tendencies, etc.

Question b.
What are the problems in areas of low population densities?
Answer:
The following are the problems in areas of low population densities:

1. Shortage of labour supply
2. Low levels of demand for various goods and services
3. Under utilization of resources, etc.

Give it a try:

Question a.
How do imbalanced sex ratios affect the society?
Answer:
Imbalanced sex ratios affect the society as follows:

1. Increased problems in society, workplace, etc.
2. Increased crimes against women.

Question b.
What measures can be taken to strike a balance in the sex ratio?
Answer:
The following measures can be taken to strike a balance in the sex ratio:

1. Increasing literacy rate of females.
2. Increasing employment opportunities for women.
3. Eradicating evil social customs.
4. Launching government schemes of women empowerment.

Balbharti Maharashtra State Board Class 8 Geography Solutions Chapter 5 Ocean Currents Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Geography Solutions Chapter 5 Ocean Currents

Class 8 Geography Chapter 5 Ocean Currents Textbook Questions and Answers

1. Choose the correct option:

Question a.
In which ocean does the Labrador current flow?
(a) Pacific
(b) South Atlantic
(c) North Atlantic
(d) Indian
Answer:
(c) North Atlantic

Question b.
Which current out of the following flows in the Indian Ocean?
(a) East Australian current
(b) Peru current
(c) South Polar current
(d) Somali current
Answer:
(d) Somali current

Question c.
Which factor out of the following does not affect the region along the coast?
(a) Precipitation
(b) Temperature
(c) Land breeze
(d) Salinity
Answer:
(c) Land breeze

Question d.
Which of the following occurs in the area where the cold and warm currents meet?
(a) High temperature
(b) Snow
(c) Low temperature
(d) Thick fog
Answer:
(d) Thick fog

Question e.
Which of these following currents flow from the northern polar regiorTup to Antarctica?
(a) Warm ocean currents
(b) Surface ocean currents
(c) Cold ocean currents
(d) Deep ocean currents
Answer:
(d) Deep ocean currents

2. Examine the given statements and correct the wrong ones:

Question a.
Ocean currents give specific direction and velocity to the water.
Answer:
Correct.

Question b.
The deep ocean currents flow with high velocity.
Answer:
Correct.

Question c.
Generally, surface ocean currents are formed in the equatorial regions.
Answer:
Incorrect.
Correct statement: Generally, surface ocean currents are formed in the equatorial region as well as polar region.

Question d.
Ocean currents hold great importance for human life.
Answer:
Correct.

Question e.
The movement of icebergs is not dangerous for water transport.
Answer:
Incorrect.
Correct statement: The movement of icebergs is dangerous for water transport.

Question f.
Water becomes warm near Brazil due to ocean currents. On the other hand, it becomes cold near African coast.
Answer:
Incorrect.
Correct statement: Water becomes warm near Brazil due to ocean currents. Similarly, it also becomes warm near African coast.

3. Explain the effect of-

Question a.
Warm ocean currents on climate.
Answer:

1. The amount of precipitation increases in the coastal region along with which the warm ocean currents flow.
2. Similarly, the temperature increases in the coastal region along with which the warm ocean currents flow.

Question b.
Cold ocean currents on the movement of icebergs.
Answer:

1. Due to cold ocean currents, icebergs are moved away from the polar regions.
2. These icebergs come along the marine routes and prove hazardous to the ships.

Question c.
The shape of the coastline on ocean currents.
Answer:

1. The extended parts of coastline acts as an obstacle for ocean currents.
2. The extended parts of coastline alters the direction and velocity of ocean currents.

Question d.
Meeting of warm and cold ocean currents.
Answer:

1. Dense fog is found in the meeting point of warm and cold ocean currents. Algae, plankton, etc. fish food grow on a large scale in these areas.
2. Fish come in these areas on a large scale and breed. Therefore, extensive fishing grounds are found in the areas where warm and cold ocean currents meet.

Question e.
The transportation capacity of ocean currents.
Answer:

1. The transportation capacity of ocean currents alters the amount of precipitation and temperature in the coastal regions along with which they flow.
2. The transportation capacity of ocean currents leads to transfer of warm water to the bottom from the surface and cold water to the surface from the bottom.

Question f.
Deep ocean currents.
Answer:

1. Deep ocean currents leads to transfer of warm water to the bottom from the surface and cold water to the surface from the bottom.
2. Deep ocean currents thus leads to redistribution of sea water.

4. Look at the map of ocean currents and answer the following:

Question a.
How does the Humboldt current affect the climate of the South America?
Answer:
Humboldt current is a cold ocean current and so it decreases the amount of precipitation and temperature on the western coastal region of the South America.

Question b.
In which oceans are counter equatorial currents not observed and why?
Answer:
Counter equatorial currents are not observed in Arctic Ocean and Southern Ocean. These oceans are located near the polar regions. Therefore, the effects of trade winds is found to be less in these oceans Therefore, counter equatorial currents are not observed in these oceans.

Question c.
Which currents are absent in the northern part of the Indian Ocean and why?
Answer:
Cold currents are absent in the northern part of the Indian Ocean. The northern part of Indian Ocean is included in the temperate zone. So cold currents are absent in the northern part of the Indian Ocean.

Question d.
In which regions do the cold and warm ocean currents meet?
Answer:
The cold and warm ocean currents S meet in the following regions:

1. North Atlantic Ocean (cold Labrador current and warm Gulf stream current)
2. North Pacific Ocean (cold Oyashio current and warm ! Kurishio current)
3. South Atlantic Ocean ! (cold Falkland current and warm Brazil current)
4. South Pacific Ocean (cold South Polar current and warm East Australian current)
5. Indian Ocean (cold South Polar i current and Agulhas Current)

5. Answer the following questions:

Question a.
What are the reasons responsible for the formation of deep ocean currents?
Answer:

1. The temperature varies in various parts of ocean.
2. Similarly, the density of water in various parts of ocean is also found to be different.
3. The difference in the temperature and density of seawater leads to its circulation and the deep ocean currents are formed. This circulation is known as thermohaline circulation.

Thus, the difference in temperature and density of water in various parts of ocean are the reasons responsible for the formation of deep ocean currents.

Question b.
What is the reason behind the dynamics of the ocean water?
Answer:
Planetary winds is the reason behind the dynamics of the ocean water.

Question c.
How do winds give direction to the ocean currents?
Answer:
Winds give clockwise direction to the ocean currents in the northern hemisphere and anti-clockwise direction to the ocean currents in the southern hemisphere.

Question d.
Why do the ports in the eastern coast of Canada freeze in winter?
Answer:

1. Labrador cold current flows along the eastern coast of Canada.
2. Due to Labrador cold current, the temperature of sea water near the eastern coast of Canada decreases.
3. Due to fall in temperature, the sea water along the eastern coast of Canada start freezing. As its effect, the ports in the eastern coast of Canada freeze in winter.

Activity:

Question a.
Look for more funny and interesting information related to ocean currents.

Class 8 Geography Chapter 5 Ocean Currents Additional Important Questions and Answers

Examine the following statements and correct the incorrect ones:

Question a.
Labrador is a warm ocean current.
Answer:
Incorrect.
Correct statement: Labrador is a cold ocean current.

Question b.
Surface ocean currents flow with high velocity.
Answer:
Incorrect.
Correct statement: Surface ocean currents flow with slow velocity.

Question c.
Even though the velocity of ocean currents is less, the water carried by them is immense.
Answer:
Correct.

Question d.
The ocean currents flow near the lower boundary of the continental shelf.
Answer:
Correct.

Answer the following questions in one sentence each:

Question a.
What are the main types of ocean currents?
Answer:
Cold ocean currents and warm ocean currents are the main types of ocean currents.

Question b.
In which region are the warm ocean currents formed?
Answer:
The warm ocean currents are formed in the equatorial region.

Question c.
In which regions are the cold ocean currents formed?
Answer:
The cold ocean currents are formed in the polar regions.

Question d.
Which factors are responsible for the formation of ocean currents?
Answer:
Difference in temperature of seawater, difference in density of seawater and planetary winds are the factors responsible for the formation of ocean currents.

Question e.
Which factors are responsible for the direction of flow and velocity of ocean currents?
Answer:
Rotation of the earth and continental structure are the factors responsible for the direction of flow and velocity of ocean currents.

Question f.
In which unit is the discharge of water in the oceans measured?
Answer:
The discharge of water in the oceans is measured in the Sverdrup unit.

Question g.
What is meant by 1 Sverdrup discharge?
Answer:
1 Sverdrup discharge means 1 million cu.m./second discharge of ocean water.

Question h.
Which two ocean currents meet near Newfoundland Island?
Answer:
Gulf warm ocean current and Labrador cold ocean current meet near Newfoundland Island.

Match the columns and complete the chain:

Question a.

‘A’ Column	‘B’ Column	‘C’ Column
1. California Current	i. South Atlantic Ocean	a. Near the eastern coast of the continent of North America
2. Hamboldt Current	ii. North Pacific Ocean	b. Near the eastern coast of the continent of South America
3. Brazil Current	iii. North Atlantic Ocean	c. Near the western coast of the continent of South America
4. Gulf Current	iv. South Pacific Ocean	d. Near the western coast of the continent of North America

Answer:

‘A’ Column	‘B’ Column	‘C’ Column
1. California Current	ii. North Pacific Ocean	d. Near the western coast of the continent of North America
2. Hamboldt Current	iv. South Pacific Ocean	c. Near the western coast of the continent of South America
3. Brazil Current	i. South Atlantic Ocean	b. Near the eastern coast of the continent of South America
4. Gulf Current	iii. North Atlantic Ocean	a. Near the eastern coast of the continent of North America

Answer the following questions in brief:

Question a.
Write in brief about warm ocean currents.
Answer:
1. Ocean currents that move water away from the Equator to the poles are called warm ocean currents.
2. Warm ocean currents are formed in the equatorial region and they flow towards the poles.

3. The warm currents increase the temperature and precipitation in the coastal areas along with which they flow. For example, the warm ocean currents flowing along with the coastal areas of Western Europe, Southern Alaska and Japan increases the temperature in the coastal areas along with which they flow. As its effect, the ports in the coastal areas of Western Europe, Southern Alaska and Japan do not freeze in winter.

4. Gulf stream, Agulhas, Somali, etc. are some of the warm ocean currents.

Question b.
Write in brief about cold ocean currents.
Answer:
1. Ocean currents that move water away from the poles to the Equator are called cold ocean currents.
2. Cold ocean currents are formed in the polar region and they flow towards the equatorial region.

3. The cold currents decrease the temperature and precipitation in the coastal areas along with which they flow. For example, the cold ocean currents flowing along with the coastal areas of Peru, Chile, and southeastern Africa, decreases the amount of precipitation in the coastal areas along with which they flow. As its effect, arid desert areas are formed in Peru, Chile, and southwestern Africa.

4. Falkland, Labrador, Canary, Oyashio, Benguela, etc. are some of the cold ocean currents.

Question c.
Write in brief about conveyor belt.
Answer:

1. Due to deep ocean currents, the warm water goes down and the cold water comes to the surface of the earth.
2. Thus, deep ocean currents redistribute the ocean water.
3. This redistribution of ocean water takes around 500 years to complete.
4. This redistribution (movement) of sea water is known as conveyor belt.

Question d.
Write in brief about relation between ocean currents and fishing.
Answer:

1. Algae, plankton, etc. fish food grow on a large scale in the areas where warm ocean current and cold ocean current meet.
2. Fish come in these areas on a large scale and breed. Therefore, extensive fishing
   grounds are found in the meeting point of warm and cold ocean currents.
3. For example, Grand Bank in Atlantic Ocean near the coastal region of North America, Dogger Bank near the continent of Europe, etc.

Explain the effect of the following:

Question a.
Cold ocean currents on climate.
Answer:

1. The amount of precipitation decreases in the coastal region along with which the cold ocean currents flow.
2. Similarly, the temperature decreases in the coastal region along with which the cold ocean currents flow.

Give geographical reasons:

Question a.
Fog is found near Newfoundland island.
Answer:

1. Fog is found at the meeting point of warm and cold ocean currents.
2. Warm Gulf Stream ocean current and cold Labrador ocean current meet near Newfoundland island. Therefore, fog is found near Newfoundland island.

Question b.
Ocean transport is carried out along with ocean currents.
Answer:

1. Ocean transport carried out along with ocean currents increases the speed of ocean transport and so saves the time.
2. Ocean transport carried out along with ocean currents decreases the cost of fuel. Therefore, ocean transport is carried out along with ocean currents.

Question c.
Extensive fishing ground is found near Newfoundland island.
Answer:

1. Warm Gulf Stream ocean current and cold Labrador ocean current meet near Newfoundland island.
2. Algae, plankton, etc. fish food grow on a large scale in the meeting point of warm Gulf Stream ocean current and cold Labrador ocean current.
3. Fish come in this area on a large scale and breed. Therefore, extensive fishing ground is found near Newfoundland island.

Differentiate between the following:

Question a.
Cold ocean current and Warm ocean current:
Answer:

Question b.
Surface ocean current and Deep ocean current:
Answer:

Study the following map/figure /graph and answer the following questions:

Make friends with maps!

Study the Figure and answer the following questions:

Question a.
What are the major types of ocean currents?
Answer:
Warm ocean currents and cold ocean currents are the major types of ocean currents.

Question b.
What do you call the currents flowing from the equator to the poles?
Answer:
The currents flowing from the equator to the poles are called warm currents.

Question c.
What do you call the currents flowing from the poles to the equator?
Answer:
The currents flowing from the poles to the equator are called cold currents.

Question d.
When the currents are moving in a circular manner, what difference is visible in their direction in Northern and Southern Hemisphere respectively?
Answer:
When the currents are moving in a circular manner, they will move in clockwise in Northern Hemisphere and anti-clockwise in the Southern Hemisphere.

Question e.
What might happen at the places where these two currents meet?
Answer:
Dense fog will get formed at the places where these two currents meet.

Question f.
When two different types of currents meet along the coast then what type of human settlements and occupations are seen?
Answer:
When two different types of currents meet along the coast then dense human settlements and fishing occupation are seen there.

Make friends with maps!

Question a.
Where did a container full of toys fall on 10th January, 1992?
Answer:
A container full of toys fell near the Hawaii Island on 10th January, 1992.

Question b.
Where did some of the toys reach on 16th November, 1992?
Answer:
Some of the toys reached the coast of Alaska on 16th November, 1992.

Question c.
Where did some of the toys reach by the year 2000?
Answer:
Some of the toys crossed the Bering Strait and reached the Arctic Ocean by the year 2000.

Question d.
Where did some of the toys reach by the year 2003?
Answer:
Some of the toys reached the eastern coast of America by the year 2003.

Question e.
Where did some of the toys reach by the year 2007?
Answer:
Some of the toys reached the western coast of continent of Europe by the year 2007.

Question f.
Why did the toys travel in this way?
Answer:
The toys travelled in this way due to surface ocean currents and mostly due to deep ocean currents.

Thought Provoking Question:

Question a.
What will be the effect of Westerlies on the ocean currents?
Answer:

1. Due to the influence of the Westerlies, the ocean currents will flow from west to east in the mid-latitudes.
2. Due to the influence of Westerlies, the ocean currents will flow from east to west in equatorial region. This in turn, will lead to a circular pattern of sea currents.

Open-Ended Question:

Question a.
With which points will you explain the effects of ocean currents?
Answer:
The effects of ocean currents can be explained with the help of the following points:

1. Temperature: Ocean currents brings change in the temperature of the coastal areas along with which they flow. For example, the warm ocean current flowing along the coastal areas of Japan increases the temperature in the coastal areas.

2. Precipitation: Ocean currents brings change in amount of precipitation in the coastal areas along with which they flow. For example, the cold ocean current flowing along the coastal areas of Chile decreases the precipitation in the coastal areas leading to formation of desert areas.

3. Occupation: Ocean currents also supports the growth of fishing occupation. The extensive fishing grounds redeveloped the meeting point of warm and cold ocean currents. For example, Grand Bank near the continent of North America.

4. Transportation: Sea transport carried out along with ocean currents increases the speed and reduces the cost of fuel.

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 3 Force and Pressure Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 3 Force and Pressure

Class 8 Science Chapter 3 Force and Pressure Textbook Questions and Answers

1. Write proper word In the blank space:

Question a.
The SI unit of force is the ………..
(dyne, newton, joule)
Answer:
The SI unit of force is the newton.

Question b.
The air pressure on our body is equal to the …………. pressure.
(atmospheric, sea bottom, space)
Answer:
The air pressure on our body is equal to the atmospheric pressure.

Question c.
For a given object, the buoyant force in liquids of different ………… is ………….. .
(the same, density, different, area)
Answer:
For a given object, the buoyant force in liquids of different density is the same.

Question d.
The SI unit of pressure is ………………
(N/m³, N/m², kg/m², Pa/m²)
Answer:
The SI unit of pressure is N/m².

2. Make a match.

Question a.

Group ‘A’	Group ‘B’
1. Fluid	a. Higher pressure
2. Blunt knife	b. Atmospheric pressure
3. Sharp needle	c. Specific gravity
4. Relative density	d. Lower pressure
5. Hectopascal	e. Same pressure in all directions

Answer:

Group ‘A’	Group ‘B’
1. Fluid	e. Same pressure in all directions
2. Blunt knife	d. Lower pressure
3. Sharp needle	a. Higher pressure
4. Relative density	c. Specific gravity
5. Hectopascal	b. Atmospheric pressure

3. Answer the following questions in brief. 

Question a.
A plastic cube is released in water. Will it sink or come to the surface of water?
Answer:
It will come to the surface of water.
[Note: This is because its density is less than that of water. When it floats, the unbalanced force acting on it is zero.]

Question b.
Why do the load carrying heavy vehicles have large number of wheels?
Answer:
The pressure produced by a given force depends on the area of the surface on which the force acts. The greater the surface area, the less is the pressure produced. Load carrying heavy vehicles have large number of wheels so that the load (weight, force) is distributed over large surface area of the wheels in contact with the road. Hence, the pressure decreases and the tyres do not burst.

Try this :
Pressure of a liquid:

Activity 1:
Take a plastic bottle. Take a 10 cm long piece of a glass tube on which a rubber balloon can be fitted. Warm up one end of the glass tube and gently push it into the bottle at about balloon inflates. What is observed? The pressure of water acts on the side of the bottle as well.

[Note: Here, the area of cross section of the tube remains the same. As the level of the water in the bottle rises, the mass of the water increases resulting in increase in the weight. As the applied force increases, the pressure increases. Therefore, the balloon increases in size.]

Activity 2:
Take a plastic bottle. Pierce it with a thick needle (or with a hot nail) at the points 1, 2, 3 as shown in the Fig. Fill water in the bottle up to full height. A shown in the figure, water jets will be seen emerging and projecting out. The water jet emerging from the hole at the top will fall closest to the bottle. The jet from the lowest hole falls farthest from the bottle.

Also, jets coming out from the two holes at the same level fall at the same distance from the bottle. What is understood from this? At any one level, the liquid pressure is the same. Also, the pressure increases as the depth of the liquid increases.

Question c.
How much pressure do we carry on our heads? Why don’t we feel it?
Answer:
The air pressure at the sea level is about 101 × 10³ Pa. This is the pressure that we carry on our heads. The cavities in our body are filled with air, and arteries and veins are filled with blood. Their pressure balances the pressure due to the atmosphere. Hence, we don’t feel the atmospheric pressure.

4. Why does it happen?

Question a.
Why does it happen? A ship dips to a larger depth in freshwater as compared to marine water.
Answer:
The buoyant force acting on a body is proportional to the density of the fluid in which the body is immersed. The density of freshwater is less than that of marine water. Hence, the buoyant force on a body in freshwater is less than that in marine water. Therefore, a ship dips to a larger depth in freshwater as compared to marine water.

Question b.
Why does it happen? Fruits can easily he cut with a sharp knife.
Answer:

1. It is easy to cut vegetables. fruits with a sharp knife. A blunt knife does not work here.
2. The force exerted perpendicularly on a unit area is called ‘pressure’
   
3. Presently we are considering only the force acting on an area in a direction perpendicular to it.

Question c.
Why does it happen? The wall of a dam is broad at its base.
Answer:
1. The pressure at a point in a liquid is proportional to the height of the liquid column above it. Hence, the pressure of water in a dam is much greater at the bottom of the dam than at the top.
2. To withstand this high pressure, the wall of a dam is made stronger and thicker (broad) at the base than at the top.

Question d.
Why does it happen? If a stationary bus suddenly speeds up, passengers are thrown in the backward direction.
Answer:
1. When passengers sit or stand in a stationary bus, they are in a state of rest. When the bus suddenly speeds up, the lower (parts of their body in contact with the bus acquire the speed of the bus.
2. The upper parts of their body, however, continue to be in the state of rest due to inertia. Hence, they are thrown in the backward direction.

5. Complete the following tables. 

Question a.

Answer:
Using the formula,
density = mass/volume:

Mass (Kg)	Volume (m3)	Density (Kg/m3)
350	175	2
760	190	4

Question b.

Answer:
Using the formula, relative density = density of a metal/density of water:

Density of Metal (Kg/m3)	Density of water (Kg/m3)	Relative Density
5 × 103	103	5
8.5 × 103	103	4

Question c.

Answer:
Using the formula, pressure = weight/area:

Weight (N)	Area (m2)	Pressure (N.m-2)
800	0.04	20000
1500	500	3

6. The density of a metal is 10.8 × 10³ kg/m³. Find the relative density of the metal.

Question a.
The density of a metal is 10.8 × 10³ kg/m³. Find the relative density of the metal.
Solution:
Data: Density of the metal = 10.8 × 10³ kg/m³
density of water = 10³ kg/m³
relative density of the metal = ?

The relative density of the metal = 10.8.

7. The volume of an object is 20 cm³ and the mass is 50 g. The density of water is 1 gm^-3. Will the object float on water or sink in water?

Question a.
The volume of an object is 20 cm³ and the mass is 50 g. The density of water is 1 gm^-3. Will the object float on water or sink in water?
Solution :

It is greater than the density of water.
Hence, the object will sink in water.

8. The volume of a plastic-covered sealed box is 350 cm³ and the box has a mass 500 g. Will the box float on water or sink in water? What will be the mass of water displaced by the box?

Question a.
The volume of a plastic-covered sealed box is 350 cm³ and the box has a mass 500 g. Will the box float on water or sink in water? What will be the mass of water displaced by the box?
Solution:

It is greater than that of water.
Hence, the box will sink in water.
The volume of water displaced by the box (V) = the volume of the box = 350 cm³

∴ The mass of water displaced by the box = 1 g.cm^-3 × 350 cm³ = 350 g.

Project:

Question a.
Video record all the experiments (Try it) in this chapter with the help of mobile phone and send to others.

Class 8 Science Chapter 3 Force and Pressure Additional Important Questions and Answers

1. Rewrite the sentences after filling the blanks

Question 1.
The tendency of an object to remain in its existing state is called its …………. .
Answer:
The tendency of an object to remain in its existing state is called its inertia.

Question 2.
Pressure = ……………
Answer:

Question 3.
1 bar = ……………….. N/m².
Answer:
1 bar = 10⁵ N/m².

Question 4.
1 atmosphere = ………….. Pa.
Answer:
1 atmosphere = 101 × 10³ Pa.

Question 5.
The SI unit of density is …………. .
Answer:
The SI unit of density is kg/m³

Write proper word In the blank space:

Question 1.
According to Archimedes’ principle, the magnitude of the force of buoyancy acting on a body is …………. .
(Vρg, Vρ/g, Vρm, mρg)
Answer:
According to Archimedes’ principle, the magnitude of the force of buoyancy acting on a body is Vρg.

Question 2.
The pascal is the unit of ……………. .
(velocity, pressure, mass, force)
Answer:
The pascal is the unit of pressure.

Question 3.
Keeping the surface area constant, if the applied force is doubled, the pressure …………….. .
(becomes double, remains the same, becomes four times, becomes half)
Answer:
Keeping the surface area constant, if the applied force is doubled, the pressure becomes double.

State whether the following statements are True or False:

Question 1.
The density of water is 1000 g/cm³.
Answer:
False. [The density of water is 1000 kg/m³ (or 1 g/cm³)]

Question 2.
Force and weight have the same units.
Answer:
True.

Question 3.
Atmospheric pressure at sea level is about 10⁶ dynes/cm².
Answer:
True.

Question 4.
The buoyant force due to a liquid is proportional to the acceleration due to gravity.
Answer:
True.

Question 5.
Atmospheric pressure increases with altitude.
Answer:
False. (Atmospheric pressure decreases with altitude.)

Question 6.
Pressure due to a given force is directly proportional to the area on which the force acts.
Answer:
False. (Pressure due to a given force is inversely proportional to the area on which the force acts.)

Question 7.
When a body is completely immersed in a liquid, the buoyant force acting on it due to the liquid is proportional to the volume of the liquid displaced by the body.
Answer:
True.

Question 8.
The density of a material is useful to determine its purity.
Answer:
True.

Question 9.
One tends to slip over a banana peel on the street and one can slip due to mud are events that occur due to reduced friction.
Answer:
True.

Question 10.
Frictional force is electromagnetic in origin.
Answer:
True.

Identify the odd term:

Question 1.
Density, Pressure exerted by a gas, Mass, Force.
Answer:
Force. (Force is a vector quantity; other quantities are scalar quantities.)

Question 2.
Lactometer, Hydrometer, Voltmeter, Submarine.
Answer:
Voltmeter. (Its working is not based on Archimedes’ principle. The working of a lactometer, hydrometer and submarine is based on Archimedes’ principle.)

Rewrite the following table in such a way that Column 2 and Column 3 will match with Column 1:

Question 1.

Column 1	Column 2	Column 3
1. Pressure	Mass/volume	Specific gravity
2. Density	Force/area	Decreases with increase in height above the sea level
3. Atmos­pheric pressure	No unit	Useful to determine the purity of a substance
4. Relative density	The pascal	Decreases with increase in area

Answer:

Column 1	Column 2	Column 3
1. Pressure	Force/area	Decreases with increase in area
2. Density	Mass/volume	Useful to determine the purity of a substance
3. Atmos­pheric pressure	The pascal	Decreases with increase in height above the sea level
4. Relative density	No unit	Specific gravity

Answer the following questions in one sentence:

Question 1.
Which of the following has more inertia? A ₹ 10 coin and a ₹ 1 coin.
Answer:
A ₹ 10 coin has more inertia than a ₹ 1 coin.

Question 2.
Name the physical quantity expressed in pascal.
Answer:
Pressure is expressed in pascal.

Question 3.
State the SI unit of pressure.
Answer:
The SI unit of pressure is N/m², also called the pascal.

Question 4.
Name the property of a liquid due to which it exerts an upward force on an object immersed in it.
Answer:
Buoyancy is the property of a liquid due to which it exerts an upward force on an object immersed in it.

Question 5.
Name the principle used in designing ships and submarines.
Answer:
Archimedes’ principle is used in designing ships and submarines.

Question 6.
What is specific gravity?
Answer:
The specific gravity of a substance is another name used for relative density, i. e., the ratio of the density of the substance to the density of water.

Question 7.
State any one factor on which the pressure exerted by a liquid at a point inside the liquid depends.
Answer:
The pressure exerted by a liquid at a point inside the liquid depends on the density of the liquid.

Question 8.
State any one factor on which the buoyant force due to a liquid depends.
Answer:
The buoyant force due to a liquid depends on the density of the liquid.

Question 9.
Name the device used to determine the purity of a sample of milk.
Answer:
The lactometer is used to determine the purity of a sample of milk.

Question 10.
Name the device used to determine the density of a liquid.
Answer:
The hydrometer is used to determine the density of a liquid.

Question 11.
Name two instruments whose working is based on Archimedes’ principle.
Answer:
Working of the lactometer and hydrometer is based on Archimedes’ principle.

Answer the following questions:

Question 1.
Give three examples to show that a force acts on two bodies through an interaction between them.
Answer:

1. Consider a car at rest on a level (plane) road. If it is pushed from behind, it moves in the forward direction.
2. Iron nails get attracted to the poles of a magnet and stick to the magnet.
3. The moon revolves around the earth.

Question 2.
What is a contact force? Give one example.
Answer:
A force that acts through a direct contact of two objects or via one more object, is called a contact force.
Example: If a ball at rest on the ground is kicked, it starts moving.

Question 3.
What is a non contact force? Give one example.
Answer:
A force that acts between two objects even if the two objects are not in contact, is called a non contact force.
Example: The earth revolves around the Sun.

Use your brainpower!
Make a list of some more examples in which contact and non contact forces are applied. Write the types of force.
Answer:
1. Some examples in which contact forces are applied:

• to cut an apple with a knife (muscular force, frictional force)
• to lift a ball lying on the ground (muscular force, frictional force)

2. Some examples in which non contact forces are applied:

• the motion of the earth around the Sun (gravitational force)
• the motion of an electron around the nucleus of an atom (mainly the electric force).

Question 4.
In the following examples, state whether the force is a contact force or non contact force:

1. a reluctant dog is being pulled by his master
2. a boy playing football is kicking the ball away
3. when iron nails are brought near a magnet, they are attracted to the poles of the magnet and stick to the magnet
4. a coconut is falling from the coconut tree
5. when a comb is rubbed against hair, small pieces of paper kept on a table get attracted to the comb
6. when brakes are applied to a moving bicycle, it stops after some time

Answer:

1. contact force
2. contact force
3. non contact force
4. non contact force
5. non contact force
6. contact force.

Question 5.
Give one example in which frictional force is useful.
Answer:
While walking, we push the ground behind with our feet. In the absence of friction between the ground and the lower surface of our feet, we will slip and will not be able to walk.
[Note: Frictional force is electromagnetic in origin.]

Try this: 
Take two plastic bottles with rectangular shape. Close their openings by fitting the lids tightly. Keep two small bar magnets on them and fix them neatly using a sticking tape.

Fill a big plastic tray with water and leave the two bottles floating with magnets at the top. Take one bottle near the other. If the north pole of the magnet is near the south pole of the other magnet, the bottles will head towards each other, because unlike poles attract each other.

Observe what will happen when the directions of the bottles are changed. We can observe change in the motion of the bottles without any direct contact. This means that there exists a non contact force between the two magnets.

Observation: When the directions of the bottles are changed, if the north pole of one magnet is near the north pole of the other magnet (or the south pole of one magnet is near the south pole of the other magnet), the bottles will move away from each other because like poles repel each other.

Use your brain power!

Question.
You have learnt about static electricity in the previous standard. Electrostatic force is a non contact force. To verify this, which experiment will you perform?
Answer:

Do not switch on the fan in the room. Keep very small pieces of paper on the table. Rub a plastic comb against hair and bring it near the bits of paper. You will find that the bits of paper are attracted by the comb. The comb, on rubbing acquires electrostatic charge. It induces opposite charges on the bits of paper. Hence, the bits of paper are attracted by the comb.

Try this: 
Balanced forces and unbalanced force:

Take a cardboard box, tie thick string to its two sides and keep it on a smooth table as shown in Fig. Take the strings on both sides of the table. Tie weighing pans to the two ends. Keep equal masses in both the pans. The box does not move on the table.

If more mass is kept in one of the pans than in the other, the box starts moving in the direction of that pan. Equal gravitational force acts on both the pans when equal masses are kept in them. This means balanced forces act on the box, with effective force equal to zero as these are acting in opposite directions.

On the contrary, if more mass is kept in one pan than in the other, the box starts moving in the direction of the pan with more mass. When unequal forces are applied to the box on the two sides, an unbalanced force acts on the box resulting in imparting motion to the box.

Children playing tug of war pull the rope in their respective directions. If the pull of the force is equal on the two sides, the rope does not move. If the force is more on one side, the rope moves in that direction. This means that initially, the two forces are balanced; the rope moves in the direction of higher force when the forces become unbalanced.

Let us see one more example. When a big grain storage container is required to slide on the ground, it becomes easier if two persons push it rather than one person. When the force is applied by both in the same direction, the movement is easy. You may have experienced this. What do we understand from this example?

1. If several forces are applied on an object in the same direction, a force equal to their addition acts on that object.
2. If two forces are applied on one object in directions opposite to each other, a force equal to their difference acts on the object.
3. A force is expressed in magnitude and direction.

Force is a vector quantity. If more than one force are acting on a body, then the effect on the body is due to the net force. When a force is applied on a stationary object it moves, its speed and direction change. Similarly, a force is required to stop an object in motion.

An object can change its shape due to force. While kneading a dough made from flour, the dough changes its shape when a force is applied. A potter applies a force in a specific direction while shaping the pot. Rubber, when stretched, expands. There are many such examples. ,

Question 6.
What are balanced forces?
Answer:
If a body is acted upon by two forces, equal in magnitude, opposite in direction and having the same line of action, the forces are called balanced forces. Here, the net force acting on the body is zero.

Question 7.
What is an unbalanced force?
Answer:
If two or more forces act on a body such that their resultant is not zero, the resultant is an unbalanced force.
[Note: Unbalanced force acting on a body = mass of the body × acceleration of the body.]

Question 8.
Explain: Force has magnitude as well as direction. OR Force is a vector quantity.
Answer:
The effect of force applied to a body depends upon how much force we supply, i.e., the magnitude of the force, and the direction in which the force is applied. Consider a ball at rest on the ground. When ; we push it, it starts rolling. The greater the applied force, the greater is the speed acquired by the ball.

Consider a body moving in a straight line, If we apply a force in the direction of motion of the body, the speed of the body increases. On the contrary, if we apply a force in the direction opposite to that of motion of the body, the speed of the body decreases. These ( examples show that force has magnitude as well as direction, i.e., force is a vector quantity.

Question 9.
Explain the term balanced forces.
Answer:
Consider a rigid body acted upon by two forces, equal in magnitude, opposite in . direction and having the same line of action. These forces are called balanced forces as their net effect on the body is zero.
Example: A glass slab kept on a table is acted upon by two balanced forces: (i) the weight of the slab acting downward and (ii) the upward force on the slab due to the table. Their net effect on the slab being zero, the slab remains at rest.

Question 10.
Explain the term unbalanced force.
Answer:
A single force acting on a body is an unbalanced force. It produces acceleration in the body. If two or more forces act on a body such that their resultant is not zero, the resultant is an unbalanced force responsible for accelerating the body.
Example: When a ball lying on the ground is hit with a bat, the ball is set in motion by the applied force.

Question 11.
What will happen if the force is removed completely when an object acquires a certain speed?
Answer:
If the force is removed completely when an object acquires a certain speed, the object will move with the velocity it has at the instant the force is removed.

For example, a body moving with constant speed along a circular path in a horizontal plane will fly tangentially in the sense of motion if the centripetal force (the force directed towards the centre of the circle) is removed completely.

Always remember:

1. The tendency of an object to remain in its existing state is called its inertia.
2. This is why an object in stationary state remains in the same state and an object in motion remain in the state of motion in the absence of an external force.

Types of inertia:

1. Inertia of the state of rest: An object in the state of rest cannot change its state of rest due to its inherent property. This property is called the inertia of the state of rest.

2. Inertia of motion: The inherent property of an object due to which its state of motion cannot change, is called its inertia of motion. For example, a revolving’ electric fan continues to revolve even after it is switched off, passengers sitting in the running bus get aerk in the forward direction if the bus suddenly stops.

3. Directional inertia: The inherent property of an object due to which the object cannot change the direction of its motion, is called directional inertia. For example, if a vehicle in motion along a straight line suddenly turns, the passengers sitting in it are thrown opposite to the direction of turning.

Try this:
Activity 1:
Take a postcard and keep it on a glass. Keep a 5 Rupee coin on it. Now skilfully push the card. The coin straight away falls in the glass. Have you ever done this?
Answer:
Yes. (Explanation: The postcard moves forward due to the applied force and then falls due to the earth’s gravitational force. In the absence of adequate frictional force between the coin and the postcard, the coin does not move forward with the postcard, but straightaway falls in the glass due to the earth’s gravitational force.)

Activity 2: Hang a half a kg mass from a stand, with a string 1. Tie another string 2 to the mass and keep it hanging. Now pull the string 2 with a jerk. The string 2 breaks but the mass does not fall. Heavy mass does not move. Now pull the string 2 slowly. The string 1 breaks and the mass fall down. This is because of the tension developed in the string 2 due to the mass.

(Explanation: (1) As no force acts on the mass, it remains at rest due to inertia. (2) The transmission of force results in the tension in the string 1. As the string 1 cannot withstand it, it breaks and the mass falls down.)

Question 12.
What are the three types of inertia?
Answer:
Types of inertia:

• inertia of rest
• inertia of motion
• inertia of direction.

Question 13.
What is inertia of rest ? Give two examples of inertia of rest.
Answer:
The inherent property of a body by virtue of which it cannot change its state of rest is called the inertia of rest.
Examples:

1. When we dust a carpet, the carpet moves but the dust particles in it remain at rest due to inertia and hence get separated from the carpet. Hence, the carpet becomes clean.
2. When a bus starts suddenly, the passengers experience a backwarderk due to inertia.

Question 14.
What is inertia of motion? Give two examples of inertia of motion.
Answer:
The inherent property of a body by virtue of which it cannot change its state of motion is called the inertia of motion.
Examples:

1. When a fan is switched off, its blades continue to rotate for some time. Due to internal friction and friction with air, the blades of the fan stop rotating after some time.
2. Passengers in a bus experience a forwarderk when the bus stops suddenly due to application of brakes.

Question 15.
What is inertia of direction? Give two examples of inertia of direction.
Answer:
The inherent property of a body by virtue of which it cannot change its direction of motion is called the inertia of direction.
Examples:

1. While sharpening a knife, sparks fly off tangentially in the sense of motion from the grinding stone.
2. When a vehicle moves, the mud particles sticking to its wheels fly off tangentially in the sense of motion. Hence, mudguards are fitted to vehicles.

Question 16.
Why do we fall sideways when we are sitting in a bus and it takes a sharp turn?
Answer:
When we sit in a bus and the bus is in motion, we are in a state of motion in the same direction. When the bus takes a sharp turn, our body tends to maintain the state of motion in the straight line due to inertia. The portion of our body in firm contact with the seat acquires the motion along the curved path, but the upper portion of our body, tends to move in the initial direction of motion. Hence, we fall sideways.

Question 17.
What happens when you shake a wet piece of cloth? Explain your observation.
Answer:

1. When we shake a wet piece of cloth, water droplets come out.
2. Initially, the wet piece of cloth is at rest. When the cloth is shaken, it is accelerated, but the water droplets in it, due to inertia, tend to maintain the state of rest. Hence, the droplets come out.

Question 18.
If brakes are suddenly applied to a moving car, the passengers in the car are pushed in the forward direction. Explain why.
Answer:
1. The passengers in a moving car have the same velocity as that of the car. When brakes are suddenly applied to the car, it stops suddenly and the lower parts of the passengers’ bodies in contact with the seats, come to rest.

2. The upper parts of their bodies, however, continue to be in a state of motion due to inertia. Hence, the passengers are pushed in the forward direction.

Question 19.
A person alighting from a moving train is likely to fall in the direction of motion of the train. Explain why.
Answer:

1. A person in a moving train has the same velocity as that of the train. After alighting from the moving train his feet come to rest on the platform.
2. However, due to inertia, the upper part of his body continues to be in a state of motion in the direction of motion of the train. Hence, he is likely to fall in the direction of motion of the train.

Try this: 

Activity 3: Take some sharp pointed nails and push them into a wooden plank by hammering on their heads. Now take? a nail and hold it with its head on the plank and hammer it down from the pointed end. When pressing the drawing pins into a drawing board, they get into the board easily. By applying a force using the thumb one can push the pins into the boards. On the contrary, while pressing ordinary pins into the board with a thumb, the thumb may get hurt.

What does this simple experiment tell?
The nail easily penetrates into wood from its pointed end. From this you will notice that when a force is applied on the head of the nail, it is easy to hammer it into the plank.
Explanation: The less the area of the surface on which the force is applied, the greater is the effect of the force.

Question 20.
Define pressure.
Answer:
The force exerted perpendicularly on a unit area is called pressure.

Use your brain power!

Question 1.
It is easy to cut vegetables, fruits with a sharp knife. A blunt knife does not work here. Why does this happen?
Answer:
The effect of a given force varies l inversely as the area of the surface on ( which the force is applied. The less the surface area, the greater is the effect of the force. The cutting edge of a sharp ’ knife has less cross sectional area relative to that of a blunt knife. Hence, it is easy to cut vegetables, fruits with a sharp knife, rather than with a blunt knife. For a given force, pressure is inversely proportional to the area of the surface on which the force acts.

Question 21.
State the formula for pressure, Hence, determine the unit of pressure.
Answer:

The SI unit of force is the newton (N) and that of area is m². Therefore, the SI unit of pressure is N/m². It is called the pascal (Pa). 1 Pa = 1 N/m².
[Note: The unit pascal is named in honour of Blaise Pascal (1623-62), French mathematician, physicist and philosopher.]

Question 22.
State the CGS unit of pressure. State the relation betweeen the SI and CGS units of pressure.
Answer:
The CGS unit of pressure is the dyne/cm².
IN = 105 dynes, 1m² = (102 cm)² = 104 cm² 1 Pa = 1 N/m² = 105 dynes/104 cm² = 10 dynes/cm².

Question 23.
State the factors on which pressure depends.
Answer:
Pressure depends on the applied force and the area of the surface on which the force is applied.

Question 24.
Explain with a suitable example that pressure varies inversely as the area of the surface on which the force is applied, if the force remains constant.
Answer:
The tip of a pointed nail has an extremely small area, while that of a blunt nail has a comparatively large area. A given force creates a large pressure on the pointed nail and it can be easily hammered into the wood, while a very less pressure is created on the blunt nail and it cannot be easily hammered into the wood.

This shows that pressure varies inversely as the area of the surface on which the force is applied, if the force remains constant. If the same force is applied to surfaces having different areas, the pressure is more on the surface having a smaller area.

[Note: The bottom surface of a camel’s feet is broad. Hence, the camel’s weight acts on a large surface area. This reduces the pressure on the sand. Hence, the camel’s feet do not penetrate deep into the sand. Therefore, it becomes easier for the camel to walk on sand.]

Question 25.
With neat diagrams, describe an experiment to show that pressure increases if the surface area is decreased, keeping the applied force the same.
Answer:
Take a brick measuring 20 cm x 10 cm x 5 cm. Take some clay in a glass trough. Add water to it and knead it into a soft dough. Place the brick on the dough with one of its faces measuring 20 cm x 10 cm in contact with the dough. Observe how deep the brick penetrates into the dough.

Clean the brick and place it on the dough with one of its faces measuring 10 cm x 5 cm in contact with the dough. Observe how deep the brick penetrates into the dough. You will find that the brick penetrates deeper in this case than that in the first case.

• In the first case, the weight of the brick acts on a surface area of 200 cm².
• In the second case, the weight of the brick acts on a surface area of 50 cm².
• This shows that pressure increases if the surface area is decreased, keeping the applied force the same.

Question 26.
State the unit for pressure used in atmospheric science. How is it related to the unit pascal?
Answer:
In atmospheric science, the unit used for pressure is the bar. 1 bar = 10 Pa (pascal).

Try this:

Question 1.
Do the activity as depicted in Figure What is seen?
Answer:
In Fig.(a), the plank is horizontal. In Fig.(b), four books are placed side by side on the plank. The plank bends slightly due to the pressure produced by the weight of the books.

In Fig.(c), the four books are placed one above the other in the middle of the plank. Here the area of the surface of the plank on which the force acts is reduced by a factor of four relative to the earlier case. Hence, the plank bends considerably.
[Note: This shows that for a given force, pressure varies inversely as the area of the surface on which the force acts.]

Use your brainpower! 

Question 1.
You must have seen a vegetable vendor carrying a basket on her head. She keeps a twisted piece of cloth on the head, below the basket. How does it help?
Answer:
Keeping a twisted piece of cloth on the head increases the area of the surface on which the weight of the basket containing vegetables acts. Hence, the pressure produced by the force (weight) is reduced and it becomes easier to carry the basket.

Question 2.
We cannot stand at one place for a long time. How then can we sleep on a place for 8 and odd hours?
Answer:
When we stand, our weight acts on relatively small surface area, resulting in increased tension on the muscles of our legs. Hence, we cannot stand at one place for a long time. When we sleep, our weight acts on relatively large surface area, resulting in comparatively reduced tension. Therefore, we can sleep on a place for 8 and odd hours.

Question 3.
For skiing on ice, why are long flat skis used?
Answer:
The pressure produced by a given force depends on the area of the surface on which the force acts. The greater the surface area, the less is the pressure produced. The skis used to slide over snow are long and flat so that the area is increased and hence the pressure is decreased. This makes it easier to slide over snow.

Question 27.
Why do the blades of a pair of scissors have sharp edges?
Answer:
The pressure produced by a given force depends on the area of the surface on which the force acts. The less the surface! area, the greater is the pressure produced, The blades of a pair of scissors have sharp edges so that the area is decreased and hence the pressure is increased. This makes cutting • an object such as cloth easier.
[Note: Answers to questions such as why is the blade of an axe sharp? or why is the blade of a saw sharp? can be written on the basis of the answer given above.]

Question 28.
Why does a needle have s sharp point?
Answer:
The pressure produced by a given force depends on the areas of the surface on which the force acts. The less the surface area, the greater is the pressure produced. A needle has a sharp point so that the area is decreased and hence the pressure is increased. This makes the action of piercing easier.

Question 29.
Why do school bags have broad shoulder straps?
Answer:
The pressure produced by a given force depends on the area of the surface on which the force acts. The greater the surface area, the less is the pressure produced. School bags have broad shoulder straps so that the weight of the bag is distributed over a large surface area thereby decreasing the pressure on the shoulders of the student carrying the bag.

Question 30.
How will the pressure change if the area is doubled keeping the force the same?
Answer:
If the area is doubled, keeping the force the same, the pressure will become half the initial pressure.

Question 31.
How will the pressure change if the force is doubled, keeping the area the same?
Answer:
If the force is doubled, keeping the area the same, the pressure will become double the initial pressure.

Question 32.
State the characteristics of the pressure due to a liquid (or a fluid in general).
OR
Write a short note on the pressure due to a liquid (a fluid in general).
Answer:
Characteristics of the pressure due to a liquid (or a fluid):

1. The pressure at a point in a liquid (or a fluid) is due to the weight of the liquid (fluid) column above that point.
2. It acts on all sides of the container.
3. At a given depth it is the same in all directions.
4. It is independent of the size and shape of the container.
5. It is proportional to the height of the liquid (fluid) column above the given point.
6. It is proportional to the density of the liquid (fluid).
7. It is proportional to the acceleration due to gravity at the given place.

[Note: The pressure exerted by a liquid (or gas or fluid) at a depth h below the free surface of the liquid = hpg, where p is the density of the liquid (or gas or fluid) and g is the acceleration due to gravity.]

Question 33.
Give two examples to show that air exerts equal pressure in all directions.
Answer:

1. When air is filled in a balloon, it acquires its characteristic shape such as round or oval.
2. When a bicycle tube is filled with air, it acquires its characteristic (tube-like) shape throughout. This shows that air exerts equal pressure in all directions.

Question 34.
Whatisafluid?Givetwoeamples.
Answer:
A fluid is a substance which can flow.
Examples:

1. Water (liquid)
2. Air (gas)

[Note: Liquids and gases together are called fluids. Gases have very low viscosity compared to liquids. A liquid with low viscosity flows easily. A liquid with high viscosity does not flow easily.]

Question 35.
Take two rubber balloons. Fill one with water and blow air into the other. Now prick both balloons with a pin. What do you observe?
Answer:
Water and air both come out of the balloons. Air escapes quickly compared to water and produces a loud sound.

Question 36.
State the characteristics of pressure exerted by a fluid.
OR
Write a short note on pressure exerted by a fluid.
Answer:
Characteristics of pressure exerted by a fluid:

1. A fluid due to its weight, exerts pressure on the base as well as the walls of the container that holds it.
2. A fluid exerts pressure on a body immersed in it.
3. The pressure exerted on any confined mass of fluid is transmitted undiminished in all directions.

[Note: The pressure exerted by a fluid is a scalar quantity.]

Question 37.
Take an empty can. Pour small quantity of water in it. Boil this water for a few minutes until the steam has driven out most of the air. Now close the can with the stopper tightly. Allow it to cool by pouring cold water over it. What do you observe?
Answer:
The can gets gradually crushed.
[Note: The steam inside the can condenses to form water as the can cools. Therefore, the pressure inside the can becomes much less than the external pressure of the air. Hence, the can gets crushed.]

Question 38.
Put a folded newspaper on a plastic bag. Blow air into the bag. What do you observe?
Answer:
The plastic bag inflates as air is blown into it. This raises the folded news¬paper put on the bag.

Question 39.
What is meant by atmospheric pressure?
Answer:
The earth is surrounded by air from all sides. This layer of air is called the atmosphere. Its density is high up to about 16 km from the earth’s surface. Beyond that, up to about 400 km, its density is very low. Air, due to its weight, exerts pressure on the surface of the earth.

The pressure exerted by air or the atmosphere surrounding the earth is known as the atmospheric pressure. It is the ratio of the weight of the air to the area of the surface of the earth. It decreases with altitude as the density of air decreases with altitude and also the weight of the air column above a given place.
[Note: At sea level the atmospheric pressure is about 105 Pa. We do not feel it because the pressure of blood and other fluids in our body balances it.]

Question 40.
State the relation between 1 atmosphere and the pascal.
Answer:
1 atmosphere = (about) 101 × 10³ Pa (pascal)
[Note: The air pressure at the sea level is (about) 1 atmosphere.
1 atmosphere = 101325 Pa.
1 bar = 10³ mbar (millibar)
1 mbar w 10³ Pa (hectopascal)
Atmospheric pressure is expressed in mbar or hectopascal (hPa).]

Use your brain power!

Question 1.
At the sea level the atmospheric pressure 101 × 10³ Pa is acting on a table top of size 1 m². Under such a heavy pressure, why doesn’t the table top crumble down?
Answer:
The air below the table top exerts pressure 101 × 10³ Pa on it in the upward direction. Hence, the table top doesn’t crumble down.

Question 41.
Think – Why?
Question i.
Some people feel their ears popping at the top of a mountain.
Answer:
Atmospheric pressure decreases with altitude. At the top of a mountain, it becomes less than the internal pressure in the ear. Hence, some people feel their ears popping at the top of a mountain.

Question ii.
Some people feel breathless as they climb higher and higher on a mountain.
Answer:
Atmospheric pressure decreases with altitude. Hence, some people feel breathless as they climb higher and higher on a mountain.

Question iii.
We can enjoy a cold-drink or fruit juice with the help of a straw but can we imagine drinking a cold-drink or fruit juice on the moon using a straw?
Answer:
When we suck air in the straw, the pressure of the air in the straw becomes less than that of the outside air on the cold drink or fruit juice in the bottle (or the glass). Hence, the cold drink or fruit juice rises in the straw and enters our mouth. We can then drink it. There is no atmosphere on the moon. Hence, it is not possible to enjoy a cold drink or fruituice on the moon by using a straw.

Question iv.
People are often advised not to carry fountain pens while travelling by air.
Answer:
The ink in a fountain pen (filled at sea level at atmosphere pressure) may come out through its mouth while travelling by air if the outside pressure becomes less than the pressure in the ink holder of the pen. This can spoil the clothes/purse/bag. Hence, people are often advised not to carry fountain pens while travelling by air.

Question 42.
Why do some people have earache when they travel by an aeroplane?
Answer:
When an aeroplane descends at a high speed, there is an increase in air pressure. This increases the pressure on the ear drum. Hence, some people have earache when they travel by an aeroplane.

Question 43.
Explain why a person may bleed from the nose when at a great height above the sea level.
Answer:
The pressure exerted by the blood in blood capillaries is slightly more than the atmospheric pressure and acts in a direction opposite to that of the atmospheric pressure. Atmospheric pressure decreases with height and at a great height above the sea level, it is very low.

As a result, there arises a difference in the internal and external pressures on the walls of the cells and blood capillaries. If the difference is large, it may cause the cell wall and the blood capillaries to burst. Thus, the capillaries in the nose (and ear) may burst causing bleeding.

Question 44.
When a rubber sucker is pressed onto a flat glass surface, it sticks tightly on the surface. Why? You need a large force to separate it from the surface. Why?
Answer:
When a rubber sucker is pressed onto a flat glass surface, practically all the air between the surfaces of the sucker and the glass is pushed out. The air pressure there becomes much less than the atmospheric pressure. Hence, the sucker sticks to the glass due to the external atmospheric pressure. The atmospheric pressure is about 105 Pa. It is very large. Hence, to work against it to separate the sucker from the glass, a large force is needed.

Question 45.
Describe a simple experiment to demonstrate atmospheric pressure.
Answer:
Fill a glass completely with water (to its brim) and cover it with a flat and stiff card paper (or a piece of glass). Holding your palm on the card, turn the glass upside down and take the palm away from the card.

You will find that the water does not spill. The atmospheric pressure on the card (acting upward) is greater than the pressure of the water in the glass (acting downward). Hence, the water in the glass does not spill.

Question 46.
Explain the working of an ink dropper.
[Application]
Answer:
An ink dropper consists of a tube of glass or plastic, with one end tapering to a narrow opening and the other end fitted with a small rubber bulb. When the narrow open end is dipped into the ink and the rubber bulb is pressed, some air in the tube escapes through the open end. This reduces the air pressure inside the dropper.

On releasing the bulb, the atmospheric pressure on the ink pushes the ink into the dropper. The dropper is then taken out and its open end is held over the open barrel of the pen. The bulb is then pressed so that the ink in the dropper enters the pen.
[Note: The medicine dropper works in the same manner.]

Question 47.
Why is the opening of a dropper very narrow?
Answer:
The pressure produced by a given force is inversely proportional to the area of the surface on which the force acts. The opening of a dropper is very narrow. Hence, its area of cross-section is very small. As a result, even if the dropper has a small amount of ink it, its pressure can equal the atmospheric pressure. As the opening is narrow, it is easier to transfer the ink to the pen. The possibility of ink spilling is very low.

Question 48.
What is the characteristic of the cap of eye drop bottles?
Answer:
The cap of an eye drop bottle is fitted with a dropper.

Question 49.
Explain the working of a syringe
used by children when they play with coloured water. [Application]
Answer:
As shown in the figure, a syringe used by children when they play with coloured water consists of a cylinder made of plastic or metal fitted with a piston. One end of the cylinder is in the form of a narrow

tube. The snugly fitting piston can slide in , and out smoothly. The rod connected to the i piston passes through a hole in the centre of the lid and has a handle at the other end. When the tip of the narrow tube is dipped in coloured water (or any other liquid) and the piston is pushed towards the tip, up to the bottom, most of the air in the cylinder escapes through the tube, reducing the pressure.

When the piston is moved up, the coloured water rises in the part of the cylinder below the piston due to the atmospheric pressure. Finally, the inner pressure equals the atmospheric pressure and no more coloured water enters in or comes out.

To spray the coloured water, the tube is taken out and the piston is moved towards the opening of the tube. As the inner pressure is now greater than the atmospheric pressure, the coloured water gushes out of the narrow opening of the tube.

Question 50.
How does the doctor’s syringe work?
Answer:
As shown in the figure, a syringe used by children when they play with coloured water consists of a cylinder made of plastic or metal fitted with a piston. One end of the cylinder is in the form of a narrow

tube. The snugly fitting piston can slide in , and out smoothly. The rod connected to the i piston passes through a hole in the centre of the lid and has a handle at the other end.

When the tip of the narrow tube is dipped in coloured water (or any other liquid) and the piston is pushed towards the tip, up to the bottom, most of the air in the cylinder escapes through the tube, reducing the pressure. When the piston is moved up, the coloured water rises in the part of the cylinder below the piston due to the atmospheric pressure.

Finally, the inner pressure equals the atmospheric pressure and no more coloured water enters in or comes out. To spray the coloured water, the tube is taken out and the piston is moved towards the opening of the tube. As the inner pressure is now greater than the atmospheric pressure, the coloured water gushes out of the narrow opening of the tube.

The tip of a syringe is fitted with a very fine and hollow needle. The required quantity of medicine can be taken in the syringe with the help of the piston. The medicine can then be injected into the body of a patient using the needle and the piston.

Question 51.
Explain the origin of pressure due to a gas enclosed in a container.
Answer:
Molecules of a gas are in a state of continuous random motion. These molecules possess energy due to motion. When the molecules collide with a wall of the container, they rebound. A large number of molecules collide with the wall every second. Hence, a significant force is exerted on the wall. Pressure is the force per unit surface area. Thus, a pressure is exerted by the gas on a wall of the container.

Try this: 

Buoyant force:
Take a plastic bottle and fix the lid tightly. Now place it in wafer and see. It will float on water. Try and push it into the water. Even when pushed, it continues to float. This experiment can also be done with a plastic hollow ball. Now fill the bottle with water to the fullest capacity and close the lid, and release in water. The bottle will float inside the water. Why does this happen?

The empty plastic bottle floats on the surface of water. On the contrary, the bottle full of water floats inside water but does not go to the bottom. The weight of the empty bottle is negligible as compared with the weight of the water inside.

Such a bottle with water neither floats on the surface, nor does it go to the bottom. This means the force due to gravity acting downwards (fg), must have been balanced by an opposing force in the upward direction (fb) on the bottle filled with water. This force must have originated from the water surrounding the bottle. The upward force acting on the object in water or other fluid or gas is called buoyant force (fg).

Question 52.
Define buoyant force.
Answer:
The upward force acting on the object in water or other fluid or gas is called the buoyant force.

Question 53.
State the factors on which the buoyant force depends.
Answer:
The buoyant force depends upon the volume of the object immersed in the fluid (V), the density of the fluid (ρ1) and the acceleration due to gravity (g) at that place.
[Note: Magnitude of the buoyant force = Vρ1 g.]

Use your brain power!

Question.
While pulling a bucket from a well, the bucket full of water immersed fully in water appears to weigh less than when it has been pulled out of water. Why?
Answer:
1. When a bucket full of water is immersed in water, the net force acting on the bucket = weight of the bucket full of water-the buoyant force exerted by the water on the bucket. The buoyant force due to a fluid is proportional to the density of the fluid.

2. The density of water is much greater than that of air. Therefore, the buoyant force acting on a bucket full of water while it is in water is much greater than that when it is out of water, i.e., in air. Hence, it appears to weigh less, while it is in water than when it has been pulled out of water.

Try this:

Question 1.
Take a piece of thin aluminum sheet and dip it in water in a bucket. What do you observe?
Answer:
It sinks in the water.

Question 2.
Now shape the same piece of aluminium into a small boat and place it on the surface of water. It floats, isn’t it?
Answer:
Yes, the boat floats on the surface of water.

Question 54.
A lemon sinks in a glass filled with water but it floats when we stir in two spoons of salt in the water. Explain why.
Answer:
When salt is dissolved in water, the density of the water increases. The buoyant force is proportional to the density of the liquid. Hence, when the lemon is immersed in the water containing salt, the magnitude
of the buoyant force acting on the lemon becomes greater than the magnitude of the weight of the lemon. Therefore, it floats in water.

Do you know?

How is it decided that an object left in a liquid will get sink in the liquid, will float on the surface, or will float inside the liquid?
1. The object floats if the buoyant force is larger than its weight.
2. The object sinks if the buoyant force is smaller than its weight.
3. The object floats inside the liquid if the buoyant force is equal to its weight. Which forces are unbalanced in the above cases?
Answer:
Unbalanced force:
1. Magnitude of the unbalanced force acting on the object = magnitude of the buoyant force on the object-magnitude of the weight of the object. The direction of the unbalanced force is the direction of the buoyant force.

2. Magnitude of the unbalanced force on the object = magnitude of the weight of the object – magnitude of the buoyant force on the object. The direction of the unbalanced force is the direction of the weight of the object.

3. Here, the unbalanced force is zero.

Try this:

Take a long rubberband and cut it at one point. At one of its ends tie a clean washed stone or a 50 g weight as shown in Figure
Now hold the other end of the rubberband and make a mark there. Keep the stone hanging in air and measure the length of the rubberband from the stone to the mark made earlier.

Now take water in a pot and hold the rubberband at such a height that the stone sinks in it. Again measure the length of the rubberband up to the mark. What is observed? This length is shorter than the earlier length. While dipping the stone in water, length of the stretched rubber gets slowly reduced and is minimum when it sinks completely. What could be the reason for a shorter length of the rubberband in water?

When the stone is sunk in water, a buoyant force acts on it in the upward direction. The weight of the stone acts downwards. Therefore, the force which acts on it in the downward direction is effectively reduced.
(This decreases the downard force on the rubberband. Hence, its length decreases.)

Question 55.
State Archimedes’ principle.
Answer:
Archimedes’ principle: When an object is partially or fully immersed in a fluid, a force of buoyancy acts on it in the upward direction. This force is equal to the weight of the fluid displaced by the object.
[Note: The two forces mentioned here are equal in magnitude and opposite in direction.]

Question 56.
Using Archimedes’ principle, determine the magnitude of the buoyant force.
Answer:
Let m = mass of the body (object) immersed in the fluid, V = volume of the body, ρ = density of the body, ρ1 = density of the fluid, g = magnitude of the acceleration due to gravity. Suppose that the body is completely immersed in the fluid. Then the volume of the fluid displaced by the body = V. According to Archimedes’ principle, magnitude of the buoyant force = magnitude of the weight of the fluid displaced by the body = mass of the displaced fluid × g = volume of the displaced fluid × density of the fluid × g
(as density = mass/volume)

If the body is partially immersed in the fluid, the volume of the fluid displaced by the immersed part of the body = xV ; here 0 < x < 1.
In this case, the magnitude of the buoyant force

Question 57.
Using the formula for the magnitude of the buoyant force, state under what conditions the body will
1. sink in the fluid
2. float in the fluid
3. remain in equilibrium anywhere within the fluid.
Answer:
Magnitude of the buoyant force on the body = mg \(\left(\frac{\rho_{1}}{\rho}\right)\)
= magnitude of the weight of the body × \(\left(\frac{\rho_{1}}{\rho}\right)\)
1. If the density of the fluid (ρ1) is less than the density of the body (ρ), the magnitude of the buoyant force on the body will be less than the magnitude of the weight of the body. Therefore, the body will sink in the fluid.|

2. If the density of the fluid is greater than that of the body, the magnitude of the buoyant force on the body will be greater than that of the weight of the body. Therefore, the body will float in the fluid.

3. If the density of the fluid is equal to that of the body, the magnitude of the buoyant force on the body will be equal to that of the weight of the body. Therefore, the body will remain in equilibrium anywhere within the fluid.

Use your brain power!

Question.
Explain the observations in the earlier experiments according to the Archimedes’ principle.
Answer:
The increase in the length of the rubberband (y) is proportional to the downward force (f) acting on it.
1. When the stone tied to the rubberband is hanging in air, the magnitude of the buoyant force exerted by air on the stone is negligible compared to that of the weight of the stone. Hence, ignoring it, we have f = fg = mg, where m is the mass of the stone and g is the acceleration due to gravity.

2. When the stone is immersed partially in water, f = fg – fb, where fb is the magnitude of the buoyant force exerted by water on the stone.
Now, fg = Vρg and fb = xVρwg, where V = volume of the stone, ρ = density of the stone, xV= volume of the water displaced by the part of the stone immersed in water = volume of the part of the stone immersed in water (x < 1) and ρ = density of water.

This shows that as the stone is gradually lowered in water, x goes on increasing and hence/goes on decreasing. Therefore, elongation (y) of the rubberband goes on decreasing, i.e., the length of the rubberband goes on decreasing.

3. When the stone is completely immersed in water, x becomes maximum, equal to 1. Here, f = fg \(\left(1-\frac{\rho_{\mathrm{W}}}{\rho}\right)\). This is the minimum value of. Here, the elongation of the rubberband is minimum, i.e., the length of the rubberband is minimum.

Question 58.
State the applications of Archimedes’ principle.
Answer:
Archimedes’ principle is used in the construction of ships and submarines. The working of the lactometer and hydrometer is based on Archimedes’ principle.
[Note: The hydrometer is used to determine the density or relative density of a liquid.]

Question 59.
If a spring balance is used to weigh a body, will the weight of the body be the same in vacuum and air? Explain why.
Answer:
When a body is suspended in air, the buoyant force acts on the body. Hence, the magnitude of the net downward force on 1 the body = the magnitude of the weight of the body – the magnitude of the buoyant force on the body. Hence, when a spring balance is used to weigh a body, the weight of the body in air is less than that in vacuum.

Question 60.
What is density of a substance? I Obtain its SI unit.
Answer:
The density of a substance is the ratio of its mass to volume.
The SI unit of density = \(\frac{\text { the SI unit of mass }}{\text { the SI unit of volume }}\) = kg/m³
[Note: Density is useful in determining the purity of a substance. The CGS unit of density is g/cm³.
1 kg/m³ = 10³g/(100 cm)³ = 10^-3g/cm³
∴ 1g/cm³ = 1000 kg/m³]

Question 61.
What is relative density of a substance?
Answer:
The relative density of a substance is the ratio of its density to the density of water.
[Note: Relative density is also called specific gravity. It is a ratio of two equal (same) physical quantities. Hence, it has no unit.]

Question 62.
A piece of wood floats both in water and kerosine. In which liquid does it sink more during floating? Why?
Answer:
The piece of wood sinks more in kerosine than in water during floating. The density of kerosine is less than that of water. The buoyant force on a body is proportional to the density of the liquid in which the body is immersed. When a body floats, the magnitude of the buoyant force acting on the body is equal to that of the weight of the body.

Hence, the volume of the liquid displaced by a floating body is inversely proportional to the density of the liquid. As a result, when a piece of wood floats in kerosine, it displaces greater volume of kerosine compared to the volume of water displaced when the piece of wood floats in water. Hence, it sinks more in kerosine than in water.
[Note: When a body floats in a liquid fb = fg
∴ Vρ1g = Vbρbg
∴ The volume of the liquid displaced by the body is V = Vb \(\frac{\rho_{\mathrm{W}}}{\rho_{1}}\), where Vb is the volume of the body, ρb is the density of the material of the body and ρ1 is the density of the liquid. Thus, V ∝ 1 /ρ1]

Question 63.
State whether the body will float or sink in a liquid if the density of the body is 1. greater than that of the liquid 2. less than that of the liquid 3. equal to that of the liquid.
Answer:

1. The body will sink in the liquid if the density of the body is greater than that of the liquid.
2. The body will float in the liquid if the density of the body is less than that of the liquid.
3. The body will float inside the liquid if the density of the body is equal to that of the liquid.

Question 64.
If the relative density of a body is greater than 1, will it float in water?
Answer:
If the relative density of a body is greater than 1, it will not float in water.
[Note: The relative density of a pin is much greater than 1. But when kept gently on the surface of water, it floats. This is due to the surface tension of water.]

Question 65.
A glass of water has an ice cube floating in water. The water level must touches the rim of the glass. Will the water overflow when the ice melts? Give the reason.
Answer:
The water will not overflow when the ice melts. The water level will remain the same. Ice floats on water because its density is less than that of water. When ice melts, the volume of the water formed is less than the volume of the ice which has melted.

When ice in water melts, this difference equals the volume of the water formed when the part of ice above the surface of water melts. Therefore, the water level remains the same. Hence, there is no overflow of water when the ice melts.

Question 66.
A plastic ball is released underwater. State whether it will sink or come up to the surface of water. Give the reason.
Answer:
A plastic ball released under water will come up to the surface of water. The density of water is greater than that of plastic. Hence, when a plastic ball is under water, the magnitude of the buoyant force exerted by water on the ball is greater than the magnitude of the weight of the ball.

Therefore, the ball will start moving upward. As it comes up with part of the ball above the water surface, the volume of the water displaced by the ball becomes less and hence at a certain stage, the buoyant force and the weight balance each other. Then the ball continues to remain in that state, as the net force on the ball becomes zero.
[Note: Initially, the ball moves slightly up and down near the water surface. The force due to friction with water, opposing the motion of the ball, finally makes the ball steady.]

Write short notes:

Question 1.
Buoyant force.
Answer:
1. When a body is immersed partially or completely in a liquid, the liquid exerts forces on all sides of the body. This force is perpendicular to the surface of the body and equals the product of pressure and area at that point.

2. The resultant of all these forces acts upward. It is called the upthrust or buoyant force.

3. The buoyant force is proportional to (i) the volume of the liquid displaced by the body (ii) the density of the liquid (iii) the acceleration due to gravity. Its magnitude equals the magnitude of the weight of the liquid displaced by the body.

Question 2.
Applications of Archimedes’ principle.
Answer:
1. The working of a lactometer, a device used to determine the purity of a sample of milk, and a hydrometer, a device used to determine the density of a liquid, is based on Archimedes’ principle. The extent to which a lactometer floats (or sinks) depends on the density (and hence purity) of the milk. The same thing is true for a hydrometer. The greater the density of a liquid, the less is the extent to which a body sinks in it.

2. Archimedes’ principle is used in design of ships and submarines. A submarine is provided with large tanks at the front and the back. Its weight can be increased by filling the tanks with sea water or air from compressed air reservoirs. The weight can be decreased by pumping out water from the tanks by forcing compressed air in them. By controlling the weight, it can be made to sink or rise to the surface as desired.

3. The density of a body that floats or sinks in water or kerosine can be determined by. Archimedes’ principle.
4. The density of kerosine can be determined by Archimedes’ principle, using a body of material that is not affected by water and kerosine.

Give scientific reasons:

Question 1.
The tiles are placed over a slushy patch of ground to help cross It.
Answer:

1. Tiles have greater area than the area of our feet.
2. The weight of the person crossing the slushy patch is exerted over a large area of the tiles.
3. Therefore, there is a decrease in the pressure and hence the tiles do not sink much in the slushy patch of ground. This helps to cross the slushy patch of ground.

[Note: If there were no tiles, the feet will come in direct contact with the slushy ground. The area of the feet being less, the weight of the person will act over a smaller area. Therefore. there will be more pressure and hence the feet will sink into the slushy ground.]

Question 2.
Drawing pins have flattened heads.
Answer:

1. The head of a drawing pin is flattened and the other end is pointed.
2. When enough force is applied to the head of the pin, the pressure due to the force on the pointed end increases tremendously and the pin can be easily inserted in the drawing board.
3. When we press the flattened end, the force applied spreads over a larger area. This reduces the pressure of the reaction force acting on the thumb. Hence, the thumb is not injured.
4. If the head of the pin is sharp, then the pressure due to the force would be more and hence the pressure of the reaction force would also be more and the sharp end would prick the thumb causing injury.

Question 3.
An iron nail sinks in water but a ship made from iron floats on water.
Answer:
1. An iron nail sinks in water because its density is more than that of water.
2. A ship made from iron, due to the particular shape given to it, displaces a large amount of water so that the buoyant force acting on the ship due to water balances the weight of the ship. Hence, the ship floats on water.

Question 4.
A piece of iron sinks in water but floats on mercury.
Answer:
The density of iron is more than that of water but less than that of mercury. Hence, a piece of iron sinks in water but floats on mercury.

Question 5.
A sheet of metal that sinks in water can float if shaped like a pan.
Answer:

1. A sheet of metal sinks in water because its density is more than that of water.
2. If the sheet is shaped like a pan, it can displace a large amount of water such that the buoyant force on the pan due to water balances the weight of the pan. Hence, it can float on water.

Solve the following examples:

Problem 1.
(i) Calculate the pressure exerted by the wooden block when it is kept in the vertical position.
Given: The length of the wooden block is 80 cm, the breadth is 50 cm, the thickness is 20 cm and the weight is 500 N
(ii) Also calculate the pressure when the wooden block is kept in the horizontal position with its surface 80 cm × 50 cm touching the floor.

Solution:
Data: F = W = 500 N, l = 80 cm = 0.8 m, b = 50 cm = 0.5 m. h = 20 cm = 0.2 m
(i) A = bh = 0.5 m × 0.2 m = 0.1 m²

The pressure exerted in the vertical position of the block = 5000 N/m² or 5000 Pa.

(ii) A = lb = 0.8 m × 0.5 m = 0.4 m²

The pressure exerted in the horizontal position of the block = 1250 N/m² or 1250 Pa.

Problem 2.
Measure the length, breadth, height and mass of a rectangular tiffin box. Find the weight of the box and calculate the pressure in two different positions as in Ex. (1) above.
Solution:
Let l = 0.25 m, 6 = 0.1 m, h = 0.05 m, F = W= 0.5 N
(i) A = bh = 0.1 m × 0.05 m = 0.005 m²

(ii) A = lb = 0.25 m × 0.1 m = 0.025 m²

Problem 3.
A force of 1000 N is applied over an area 50 cm × 20 cm. Find the corresponding pressure.
Solution:
Data: F = 1000 N,
A = 50 cm × 20 cm = 0.5 m × 0.2 m = 0.1 m², pressure = ?

The pressure = 10 N/m².

Problem 4.
A metal block has thmensions 10 cm × 5 cm × 2 cm and the density of the metal is 8 × 10³ kg/m³. It is kept on a table with the face 10 cm × 5 cm in contact with the table. Find the force and pressure exerted by the block on the table. (g = 9.8 m/s²)
Solution :
Data : 1 = 10 cm, b = 5 cm,
h = 2 cm, p= 8 × 10 kg/m3, g = 9.8 m/s²,
A = lb = 10cm × 5cm = 50cm² = 50 × 104m²
= 5 × 10^-5m², force =?, pressure = ?
Volume of the block = lbh =
10 cm × 5 cm × 2 cm= 100 cm³
= 100 × 10^-6 m³ = 1 × 10^-4m³
Mass of the block = volume × density
(∵ density = mass/volume)
∴Mass of the block,
m = 1 × 10^-4 m³× 8 × 10³ kg/m³ = 0.8 kg
Weight of the block = mg = 0.8 kg × 9.8 m/s² = 7.84 N
∴ The force exerted by the block on the table = 7.84 N.
force 7.84 N

= 1.568 × 10³ N/m² or 1.568 × 10³ Pa
The pressure exerted by the block on the table = 1.568 × 10 N/m2 or 1.568 × 10³ Pa.

Problem 5.
A body of volume loo cm³ is immersed completely in water. Find the weight of the water displaced by the body. 1g = 9.8 m/s². p (water) = kg/m³]
Solution :
Data: V = 100 cm³ = 100 × 10^-6 m³
= 1 × 10 m³, p(water) = 10 kg/m³
g = 9.8 m/s², weight of the displaced water ?
Density = \(\frac{\text { mass }}{\text { volume }}\)
∴ Mass = volume × density
Volume of the water displaced by the body = l × 10^-4 m³
∴Mass of the water displaced,
m = l × 10^-4 m³ × 10 kg/m³ = 0.1 kg
∴Weight of the water displaced
= mg = 0.1 kg × 9.8 m/s² = 0.98 N.
The weight of the water displaced by the body = 0.98 N.

Problem 6.
A body of mass 200 g and volume 50 cm³ is put in a bucket containing water. Will it float or sink ?
[ρ(water) = 1 g/cm³]
Solution:
Data: m = 200 g, V= 50 cm³,
ρ (water) = 1 g/cm³
Density(ρ) = \(\frac{\text { mass }}{\text { volume }}\)
∴ ρ (body) = \(\frac{200}{50 \mathrm{~cm}^{3}}\)
It is greater than the density of water.
Hence, the body will sink in water.

Problem 7.
A body of mass 200 g and volume 400 cm³ is put in a bucket containing water. Will it float or sink?
[ρ (water)=1 g/cm³]
Solution:
Proceed as above.
ρ (body) = \(\frac{200 \mathrm{~g}}{400 \mathrm{~cm}^{3}}\) = 0.5 g/cm³
It is less than the density of water.
∴ The body will float in water.

Problem 8.
The mass of a tile is 500 g. If the density of the tile is 2.5 g/cm³, what will be the weight of the tile when it is completely immersed in water?
(g = 9.8 m/s², ρ(water) = 1000 kg/m³)
Solut10n:
Data: m = 500, g = 0.5 kg, ρ
(tile) = 2.5 g/cm³ = 2500 kg/m³, g = 9.8 m/s²,
ρ (water) = 1000 kg/m³, weight of the tile when completely immersed in water (also called the apparent weight) = ?
ρ = \(\frac{m}{V}\)

∴ Volume of water displaced by the tile
= 2 × 10^-4 m³
∴ Mass of water displaced by the tile
m’ = ρ (water) V = 1000 kg/m³ × 2 × 10^-4 m³
= 0.2kg
∴ Magnitude of the weight of this water
= mg = 0.2 kg × 9.8 m/s² = 1.96 N
∴ Buoyant force exerted on the tile = 1.96 N
Magnitude of the weight of the tile =
mg = 0.5 kg × 9.8 m/s² = 4.9 N
∴ Weight of the tile when completely immersed in water (apparent weight) = weight of the tile in air-buoyant force on the tile
= 4.9 N – 1.96 N = 2.94 N(downward)

Examples For Practice:

[g = 9.8 m/s², ρ (water) = 10³ kg/m³ = 1 g/cm³]

Question 1.
Calculate the relative density of a metal having density 7.5 g/cm³.
Answer:
7.5

Question 2.
Find the density of steel if its relative density is 8 and the density of water is 10 kg/m³.
Answer:
8 × 10³ g/cm³

Question 3.
A body has mass 200 g and volume 100 cm³. Find its density and relative density.
Answer:
2 g/cm³, 2

Question 4.
If the relative density of a material is 2.5, find its density.
Answer:
2.5 × kg/m³ or 2.5 g/cm³

Question 5.
A force of 100 N is applied on an area 40 cm × 25cm. Find the corresponding pressure.
Answer:
10³ N/m²

Question 6.
If the pressure exerted on an area 10 cm × 10 cm is 1000 dynes/cm², find the applied force.
Answer:
10⁵ dynes

Question 7.
A metal block of mass 10 kg is kept on a table. If the contact surface area Is 100 cm², find the pressure on the table.
Answer:
9.8 × 10³ N/m² or 9.8 × 10³ Pa

Question 8.
A body of volu.me 50 cm³ is immersed completely in water. Find the weight of the water displaced by the body.
Answer:
0.49 N

Question 9.
A block of mass 100 g and volume 20 cm³ is put in a bucket filled with water. Will it float or sink?
Answer:
The body will sink in water.

Question 10.
Will a block of mass 100g and volume 400 cm³ float or sink in water?
Answer:
The block will float in water.

Question 11.
The volume of a cube is 125 cm³ and its mass is 250 g. It is put in a tub containing water. Will it float or sink?
Answer:
It will sink in water.

Balbharti Maharashtra State Board Class 8 Geography Solutions Chapter 3 Humidity and Clouds Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Geography Solutions Chapter 3 Humidity and Clouds

Class 8 Geography Chapter 3 Humidity and Clouds Textbook Questions and Answers

1. Match the column and complete the chain: 

‘A’ Column	‘B’ Column	‘C’ Column
1. Cirrus	i. Vertical extent in the sky	a. Roaring clouds
2. Cumulonimbus	ii. Higher altitude	b. Floating clouds
3. Nimbostratus	iii. Medium altitude	c. Continuous rainfall
4. Alto-cumulus	iv Low altitude	d. Snowflake clouds

Answer:

‘A’ Column	‘B’ Column	‘C’ Column
1. Cirrus	ii. Higher altitude	d. Snowflake clouds
2. Cumulonimbus	i. Vertical extent in the sky	a. Roaring clouds
3. Nimbostratus	iv Low altitude	c. Continuous rainfall
4. Alto-cumulus	iii. Medium altitude	b. Floating clouds

2. Choose the correct word from the brackets and complete the sentences:
(Options: Cumulonimbus, relative humidity, absolute humidity, condensation, vapor-holding capacity)

Question a.
The ………….. of the air is dependent on the temperature of the air.
Answer:
vapour-holding capacity

Question b.
The amount of vapour in 1 cu.m, of air shows the ………….
Answer:
absolute humidity

Question c.
As …………. is less in the desert areas, the air is dry there.
Answer:
relative humidity

Question d.
……………. type of clouds are indicators of the storm.
Answer:
Cumulonimbus

Question e.
In a free environment, the ………….. of the vapour present in the atmosphere takes place around the dust particles.
Answer:
condensation

3. Differentiate between: 

Question a.
Humidity and clouds:
Answer:

Question b.
Relative humidity and Absolute humidity
Answer:

Question c.
Cumulus clouds and Cumulonimbus clouds
Answer:

4. Answer the following questions:

Question a.
Why is the air in a region dry?
Answer:
Due to the low amount of the moisture in the air, the air in a region is I dry.

Question b.
How is humidity measured?
Answer:
1. The amount of water vapour in 1 cu.m, of air is called the absolute humidity.

2. Absolute humidity is measured with the help the following formula:
Absolute humidity
= \(\frac{\text { Mass of water vapour }}{\text { Volume of air }}\)

3. The amount of water vapour present in air expressed as a percentage of the amount needed for saturation at the same temperature is called relative humidity.

4. Relative humidity is measured with the help of the following formula: Relative humidity (%)

Question c.
What are the prerequisites for condensation?
Answer:
High relative humidity and dew point temperature of the air are the j prerequisites for condensation.

Question d.
What is a cloud? Write its types.
Answer:
A. Meaning:
A visible mass of fine particles of ice and water accumulated around the dust particles in the air at high altitude is called a cloud.

B. Types:
The following are the types of clouds:

1. High clouds: Clouds at an altitude of 7000 m to 14000 m are considered as high clouds. Cirrus, Cirro-Stratus and CirroCumulus are high clouds.
2. Medium clouds: Clouds at an altitude of 2000 m to 7000 m are considered as medium clouds. Alto-Stratus and Alto Cumulus are medium clouds.
3. Low clouds: Clouds at an altitude of less than 2000m are considered as low clouds. Strato-Cumulus, Stratus, Nimbostratus, Cumulus and Cumulonimbus are low clouds

Question e.
Which type of clouds give rain?
Answer:
Nimbostratus and cumulonimbus type of clouds give rain.

Question f.
On what does the percentage of relative humidity depend?
Answer:
The percentage of relative humidity depends on the absolute humidity and vapour-holding capacity of the air at a given temperature.

5. Give geographical reasons:

Question a.
Clouds float in the sky.
Answer:

1. The condensed water or fine particles of snow accumulate around dust particles at high altitudes leading to formation of clouds.
2. The condensed water or fine particles in the clouds are almost weightless. Therefore, clouds float in the sky.

Question b.
The proportion of relative humidity changes according to altitude.
Answer:
1. The temperature is found to be comparatively high in the areas at sea level. Due to high temperature, moisture-holding capacity of air near sea level is found to be high. Therefore, the humidity of the air at sea level is comparatively high.

2. The temperature is found to be comparatively low in the areas at high altitude. Due to low temperature, moisture-holding capacity of air at high altitudes is found to below. Therefore, the humidity of the air at high altitude is comparatively low. In this way, the proportion of relative humidity changes according to the altitude.

Question c.
Air becomes saturated.
Answer:

1. At certain temperature, the moisture-holding capacity of air gets fulfilled and it becomes equal to the proportion of the moisture present in it.
2. At this state, no more moisture can be absorbed by the air. Thus, air becomes saturated.

Question d.
Cumulus clouds change into cumulonimbus clouds.
Answer:

1. Cumulus clouds are found between 500 m to 6000 m altitude. They are mostly formed due to the vertical flow of the air.
2. Sometimes, the vertical expanse of the cumulus clouds increases and it leads to formation of huge mountain-like cumulonimbus clouds. Thus, cumulus clouds change into cumulonimbus clouds.

6. Solve the following:

Question a.

When the temperature of the air is 30° C, its vapour-holding capacity is 30.37 gms/cu.m., If absolute humidity is 18 gms/cu.m., then what will be the relative humidity?
Answer:
Relative humidity (%)

Question b.
What would be the absolute humidity of air if 1 cu.m, air contains 4.08 gms of vapour at 0° C temperature.
Answer:
Absolute humidity

7. Collect the weather related information from newspapers for the month of July. Relate the difference in the maximum and minimum temperatures with humidity.

Activity:

Question a.
Make a table showing the types of clouds. Use various photographs.
Answer:

Class 8 Geography Chapter 3 Humidity and Clouds Additional Important Questions and Answers

Examine the following statements and correct the incorrect ones:

Question a.
Cumulonimbus clouds are the indicators of the pleasant atmosphere.
Answer:
Incorrect.
Correct statement: Cumulonimbus clouds are the indicators of the thunderstorm.

Question b.
The relative humidity is found to be high in desert region.
Answer:
Incorrect.
Correct statement: The relative
humidity is found to be less in desert region.

Question c.
The high temperature of the air leads to rapid evaporation.
Answer:
Correct.

Question d.
When the humidity in the air is 0 gm/cu.m. at any temperature, the air is said to be humid.
Answer:
Incorrect.
Correct statement: When the humidity in the air is o gm/cu.m. at any temperature, the air Is said to be dry.

Question e.
Cirrostratus appears like a bed sheet with wrinkles.
Answer:
Correct.

Answer the following questions in one sentence each:

Question a.
What is evaporation?
Answer:
The process of converting water into steam or water vapour is called evaporation.

Question b.
What is meant by the moisture-holding capacity of air?
Answer:
The capacity of air to hold moisture at a given temperature, is called the moisture-holding capacity of air.

Question c.
What is meant by the saturation of the air?
Answer:
The condition of air at a certain temperature, in which the moisture-holding capacity of air becomes equal to the I proportion of moisture present in it, is called saturation of the air.

Answer the following questions in brief:

Question a.
Write in brief about the features of high clouds.
Answer:
Clouds at an altitude of 7000 m to 14000 m are considered as high clouds. High clouds are mainly made up of ice particles. Cirrus, Cirro-Stratus and Cirro-Cumulus are high clouds. The following are the features of high clouds :

1. Cirrus: Cirrus are wispy.
2. Cirro-Stratus: Cirro-Stratus look like bed sheet with wrinkles. A halo is generally seen around these clouds.
3. Cirro-Cumulus clouds: Cirro- Cumulus look like groups of small waves.

Question b.
Write in brief about the features of medium clouds.
Answer:
Clouds at an altitude of 2000 m to 7000 m are considered as medium clouds. Alto-Stratus and Alto-Cumulus are medium clouds. The following are the features of medium clouds :

1. Alto-Stratus : Alto-Stratus are comparatively thin. The sun is visible through these clouds as if seen through a milky glass.
2. Alto-Cumulus : Alto-Cumulus are in the form of layers. They have wave-like structure. They are white in colour and have a grey shade.

Question c.
Write in brief about the features of Strato-Cumulus, Stratus and Nimbostratus.
Answer:
The features of Strato-Cumulus, Stratus and Nimbostratus are as follows :

1. Strato-Cumulus: Strato-Cumulus have layers. These clouds are mostly seen in round clusters. They are white to earthy in colour.
2. Stratus: Stratus are found in layers. They have uniform base. They are ash coloured.
3. Nimbostratus: Nimbostratus have thick layers. They are greyish in colour. They cause continuous rainfall. They are also responsible for snowfall.

Question d.
Write in brief about the features of Cumulus and Cumulonimbus.
Answer:
The features of Cumulus and Cumulonimbus are as follows :
1. Cumulus : Cumulus are found between 500 m to 6000 m altitude. They are mostly formed due to the vertical flow of the air. They have huge size and dome-like shape. They are grey in colour. They indicate pleasant atmosphere. With an increase in the vertical expanse, these clouds turn into cumulonimbus clouds and bring rain.

2. Cumulonimbus : Cumulonimbus appear like huge mountain. They are dense and dark in colour. They have anvil-like shape at the top. They are the indicators of thunder, lightning and storm. They bring rain with storm. Sometimes they also bring hailstones. The raindrops of these clouds are found to be larger in size.

Give geographical reasons for the following:

Question a.
The absolute humidity of air in coastal region is higher than humidity of air in inland areas.
Answer:
1. The rate of evaporation is found to be high in the coastal region. As its effect, the amount of moisture in air in coastal region is found to be high. This results in high absolute humidity of air in coastal region.

2. On the other hand, the rate of evaporation is found to be low in the inland areas. As its effect, the amount of moisture in air in inland regions is found to be low. This results in low absolute humidity of air in inland areas. Thus, the absolute humidity of air in coastal region is higher than humidity of air in inland areas.

Question b.
The absolute humidity of air in equatorial region is higher than humidity of air in polar region.
Answer:
1. Equatorial region receives perpendicular sunrays throughout the year leading to high temperature. High temperature increases the rate of evaporation and this further leads to high absolute humidity of air in equatorial region.

2. Polar regions receive extremely slanted sunrays throughout the year leading to very low temperature. Very low temperature decreases the rate of evaporation and this further leads to very low absolute humidity of air in polar region. Thus, the absolute humidity of air in equatorial region is higher than humidity of air in polar region.

Question c.
Damp air is found in the coastal regions.
Answer:

1. The rate of evaporation is found to be high in the coastal region. As its effect, the amount of moisture in air in coastal region is found to be high.
2. The absolute humidity of the air near coastal region is found to be high. Therefore, damp air is found in the coastal regions.

Question d.
Dry air is found in the inland regions.
Answer:

1. The rate of evaporation is found to be low in inland region. As its effect, the amount of moisture in air in inland region is found to be low.
2. The absolute humidity of the air in inland region is found to be low. Therefore, dry air is found in inland regions.

Differentiate between the following :

Question a.
Densification and Sublimation :
Answer:

Study the following map/figure /graph and answer the following questions:

1. Study the figure 3.7 given on page 20 of the textbook and answer the following questions :

Question a.
What is the maximum diameter of the raindrop?
Answer:
The maximum diameter of the raindrop is 5 mm.

Question b.
Around what does the condensation of the water vapour in the air occur?
Answer:
The condensation of the water vapour in the air occurs around the minute particles of dust or salt in the air.

2. Study the Figure 3.9 given on page 22 of the textbook and answer the following questions :

Question a.
Which type of charge is found at the upper end of the cumulonimbus clouds?
Answer:
Positive charge is found at the upper end of the cumulonimbus clouds.

Question b.
Which type of charge is found at the low end of the cumulonimbus clouds?
Answer:
Negative charge is found at the low end of the cumulonimbus clouds.

Question c.
Which type of charge is found on the land below the cumulonimbus clouds?
Answer:
Positive charge is found on the land below the cumulonimbus clouds.

Use your brainpower!

Find where the symbols given below are used while showing the weather of a place. Write their meanings in the boxes given below:
(Note: The answer is given directly.)

Question a

Answer:

Thought-Provoking Questions:

Think about it.

Question a.
During winters, when you exhale on the glass of your mirror, what happens. If you do this in summer why doesn’t it happen?
Answer:
1. During winters, the moisture-holding capacity of air is low due to low temperature. Therefore during winters, when we exhale on the glass of mirror, the condensation of water vapour present in the exhaled air takes place. As its effect very thin water drops are found on the glass of mirror.

2. During summer, the moisture-holding capacity of air is high due to high temperature. Therefore during summer, when we exhale on the glass of mirror, the water vapour present in the exhaled air gets absorbed in air. Therefore, no water drops are found on the glass of mirror.

Give it a try.

The vapour-holding capacity of 1 cu.m, of air in various temperature is given in the following table.

Calculate the difference in the capacities by observing the following table :
(Note: The answer is given directly.)

Question a.

Answer:

Temperature of the air (°C)	Vapour-holding (gm/cu.m3 (gm/cu.m3)capacity	Difference in the capacities (gm/cu.m3)
-5	3.26	—
0	4.85	1.59
5	6.80	1.95
10	9.40	2.60
15	12.83	3.43
20	17.30	4.47
30	30.37	13.07
40	51.12	20.75

Use your brain power!

Question a.
In which season is humidity generally more?
Answer:
Humidity is generally more in monsoon.

Question b.
How does the humidity affect the human body?
Answer:
The rate of respiration and sweating increases due to humidity.

Question c.
Observe how humidity affects the food materials at our home and write about the same.
Answer:
Due to humidity, fungus flourish on food materials at our home and it gets spoiled.

Question d.
Is there any relationship between formation of fungus and humidity?
Answer:
There is a direct relationship between formation of fungus and humidity. Humidity supports the growth of fungus.

Question e.
How is the early or late drying up of clothes related to humidity?
Answer:
As the moisture-holding capacity is found to be high in low humidity air, it leads to early drying up of clothes. As the moisture-holding capacity is found to be low in high humidity air, it leads to late drying up of clothes.

Think about it.

Question a.
What will happen if the temperature of saturated air at 20° C drops to 10° C abruptly?
Answer:

1. If the temperature of saturated air at 20° C drops to 10° C abruptly, the relative humidity of the air will increase abruptly.
2. Rise in the relative humidity will lead to condensation or sublimation of water vapour in the air. This in turn, will lead to precipitation or snowfall.

Open-Ended Question:

Question a.
Explain the effect of humidity on human life.
Answer:

1. High humidity increases the rate of sweating and respiration. This adversely affects the daily functioning.
2. Low humidity with pleasant atmosphere, have favourable effects on the daily routine.
3. High humidity leads to late drying up of clothes and early spoiling of food materials.
4. Low humidity leads to early drying up of clothes and late spoiling of food materials.

Balbharti Maharashtra State Board Class 8 Geography Solutions Chapter 6 Land Use Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Geography Solutions Chapter 6 Land Use

Class 8 Geography Chapter 6 Land Use Textbook Questions and Answers

1. Examine the following statements and correct the incorrect ones:

Question A.
Mining Is not type of land use.
Answer:
Incorrect.
Correct statement: Mining is a type of land use.

Question B.
There are factories in the Central Business District.
Answer:
Incorrect.
Correct statement: There are many shops, banks and offices in the Central Business District.

Question C.
In urban areas, the largest area is used for residential purposes.
Answer:
Correct.

Question D.
The village attendant issues the 7/12 extract.
Answer:
Incorrect.
Correct statement: The village talathi issues the 7/12 extract.

Question E.
In rural areas, residential areas occupy large tracts.
Answer:
Incorrect.
Correct statement: In rural areas, residential areas occupy small tracts.

Question F.
Extract 7 indicates Record of Rights.
Answer:
Correct.

Question G.
Extract 12 indicates change in ownership.
Answer:
Incorrect.
Correct statement: Extract 12 indicates tracts under cultivation.

2. Give geographical reasons.

Question A.
Land use for public facility is extremely important in urban areas.
Answer:

1. Government provides various services to fulfill the needs of citizens. The land used for fulfilling these needs is known as public utility/ facility area.
2. The lands used for post offices, police stations, public grounds, public schools, public hospitals, etc. are included public facility land use.
3. Land use for public facility increases the’ social welfare. Therefore, land use for public facility is extremely important in urban areas.

Question B.
The record of ownership of non- agricultural land is same as that of agricultural land.
Answer:
1. The record of agricultural land is maintained in the form of 7/12 extract. Similarly the record of ownership of non-agricultural land is maintained in the form of property card.

2. Like 7/12 extract, property card provides details of ownership of land, city survey number, plot number, amount of tax, area of property assessed, right to access, etc. Thus, the record of ownership of non-agricultural land is same as that of agricultural land.

Question C.
A region can be classified as developed or developing on the basis of land use.
Answer:

1. The land used in a particular region for agriculture, grazing, etc. indicates that the region is underdeveloped or developing.
2. The land used in a particular region for commercial purposes, transportation, recreation, etc. indicates that the region is developed. In this way, a region can be classified as developed or developing on the basis of land use.

3. Write answers:

Question A.
Why is agriculture important in rural land use?
Answer:

1. In India, agriculture is the main occupation of most of people in rural areas.
2. In India, farming occupation is very important as it satisfies the need of food grain and provides raw material to industries.
3. The maximum land in rural areas is used for carrying out agricultural activities. Therefore, agriculture is important in rural land use.

Question B.
State the factors affecting land use.
Answer:
(a) The factors affecting rural land use :

1. The factors like climatic conditions, fertility of soil, altitude and slope of land, irrigational facilities, natural resources, government policies, etc. affect rural land use.
2. For example, the land with gentle slope is not used for residential purpose, but is used for step farming.

(b) The factors affecting urban land use :

1. The factors like location of land, natural resources, housing development policies of government, transportation routes, industrialisation, trade and commerce, entertainment facilities, government policies, etc. affect urban land use.

2. For example, the land site near the railway station, market, etc. is mostly used for commercial purposes.

Question C.
Clarify the differences between rural and urban land use.
Answer:
The differences between rural and urban land use are as follows :

1. Land in rural areas is used for limited purposes. On the other hand, land in urban areas is used for many purposes.
2. The pattern of rural land use is comparatively simple. On the other hand, the pattern of urban land use is comparatively complex.
3. Use of land for cultivation is the major form of rural land use. On the other hand, use of land for commercial activities and residence are the major forms of urban land use.

Question D.
Differentiate between 7/12 extract and property card.
Answer:
The differences between 7/12 extract and property card are as follows :

1. 7/12 extract is issued by public revenue department of the government. On the other hand, property card is issued by city survey office of government.
2. 7/12 extract is the land record of ownership and history of ownership of the land in rural areas. Property card is the land record of ownership and history of ownership of the land in urban areas.

Activity:

Question A.
Obtain information about a town close to your village based on the following points and make a presentation in class.
(site, condition. development, land use pattern work)
a. Classify your settlement as rural or urban
b. Note the changes in land use from Central Business District outwards to the periphery in your settlement after consulting elders. Prepare a land use pattern.

Question B.
Study the 7/12 extract or the Property Card in your house and write a note.

Class 8 Geography Chapter 6 Land Use Additional Important Questions and Answers

Choose the correct answer:

Question a.
Recreational land use is use of land for …………………
(A) garden
(B) farming
(C) industry
(D) rail route
Answer:
(A) garden

Question b.
Which of the following is a planned city in India?
(A) Seoul
(B) Zurich
(C) Chandigarh
(D) Brasilia
Answer:
(C) Chandigarh

Question c.
Of which city are Bandra, Bhandup, etc. suburbs?
(A) Pune
(B) Nagpur
(C) Nashik
(D) Mumbai
Answer:
(D) Mumbai

Examine the following statements and correct the incorrect ones:

Question A.
Government policies affect the land use.
Answer:
Correct.

Question B.
The areas of mixed land use are found in cities.
Answer:
Correct.

Answer the following questions in one sentence each:

Question A.
What is meant by land use?
Answer:
Land use is the way or purpose for which land in a particular region is used.

Question B.
What is called fallow land?
Answer:
The agricultural land which is temporarily not in use is called fallow land.

Question C.
What is called forest land?
Answer:
The land which is reserved for forest area is called forest land.

Question D.
Which products are obtained from forest areas?
Answer:
The products like firewood, flowers, fruits, gum, grass, honey, etc. are obtained from forest areas.

Question E.
What is called grassland?
Answer:
The land owned by Village Panchayat or the government and which is used for grazing is called grassland.

Question F.
What is meant by commercial land use?
Answer:
Commercial land use is the use of land in urban areas for commercial purpose.

Question G.
What is meant by mixed land use?
Answer:
Mixed land use is the use of land in urban areas for more than one purpose at a time.

Answer the following questions in brief:

Question A.
How does the pattern of land use get developed?
Answer:

1. The pattern of land use gets developed through the continuous interactions between man and geographical factors.
2. The interaction between the factors like availability of land, quality of land, human needs, etc. leads to the development of specific pattern of land use.
3. For example, mineral rich land is used for carrying out mining activity.
4. For example, fertile piece of land is used for carrying out farming activity, etc.

Question B.
Write in brief about residential land use in rural areas.
Answer:

1. The density of population is found to be low in rural areas.
2. As population in rural areas is comparatively limited, the residential land use in rural areas is found to be limited.
3. In rural areas, the land close to the areas of main occupations is used for settlements.
4. For example, farmers’ residences are found near farms, fishermen’s settlements are found near coastal areas, etc.

Question C.
Write in brief about features of trAnswer:itional areas.
Answer:
The following are the features of transitional areas:

1. The intermediate areas between rural settlements and urban settlements are known as transitional areas.
2. The blend of rural and urban land use and culture is found in transitional areas.
3. Over time, trAnswer:itional areas are converted into urban areas and they are called suburbs.
4. For example, Bandra, Bhandup, etc. are the suburbs of Mumbai city.

Question D.
Write in brief about property card.
Answer:
The brief information of property card is as follows:

1. Property card is the land record of ownership and history of ownership of the land in urban areas.
2.  It is a land record of non-agricultural land.
3. Property card is issued by city survey office of government.
4. Property cards provide details of city survey number, plot number, amount of tax, area of property assessed, right to access, etc.

Answer the following questions in detail:

Question A.
Give information about arable land use and fallow land use in rural areas.
Answer:
The information about arable land : use and fallow land use in rural areas is as follows :
(a) Arable land use :

1. The use of land for cultivation is called arable land use.
2. In India, in 2011, nearly 57 per cent of land was under arable land use.
3. Generally, arable land is owned I individually.
4. The arable land can be classified on the basis of ownership of the land and types of agriculture.

(b) Fallow land use:

1. The agricultural land which is temporarily not in use is called fallow land.
2. Fallow land use is a form of rural land use.
3. To increase the fertility of soil, farmers do not use a part of agricultural land for few seasons.

Question B.
Give information about grassland use and forest land use in rural areas.
Answer:
The information about grassland use and forest land use in rural areas is as follows:
(a) Grassland land use:

1. The land owned by village panchayat or the government and which is used for grazing purpose is called grassland.
2. It is also called pastureland.
3. Mostly, grassland is owned by entire village. Very limited individual ownership of grassland is found.

(b) Forest land use:

1. The land kept reserved for forest area is called forest land.
2. Large trees, bushes, creepers and grass are found in forest land.
3. The forest products like firewood, fruits, flowers, gum, grass, honey, etc. are obtained from forest land.

Question C.
Give information about commercial land use and residential land use in urban areas.
Answer:
The information about commercial land use and residential land use in urban areas is as follows:
(a) Commercial land use:

1. The use of urban land for commercial use is called commercial land use.
2. Many shops, banks and offices are found in commercial land areas.
3. The concept of Central Business District (CBD) has emerged from commercial land use.
4. For example, Fort area or BKC (Bandra Kurla Complex) in Mumbai are the areas of commercial land use.

(b) Residential land use:

1. The use of urban land for residential purpose is called residential land use.
2. Houses and residential buildings are found in residential land areas.
3. The density of population is found to be high in urban areas. As its effect, the percentage of residential land use in urban areas is increasing day by day.

Question D.
Give information about trAnswer:port land use and public utility area in urban areas.
Answer:
The information about transport land use and Public utility area in urban areas is as follows:
(a) TrAnswer:port land use:

1. The use of urban land for providing transportation facilities is called transport land use.
2. The land used for roadways, railways, petrol pumps, vehicle repairing centres, etc. is included in transport land use.

(b) Public utility area:

1. Government provides various services to fulfill the needs of citizens. The land used for fulfilling these needs is known as public utility area.
2. Post offices, police stations, public grounds, public schools, public hospitals, etc. are included in public utility area.

Question E.
Give information about recreational land use and mixed land use in urban areas.
Answer:
The information about recreational land use and mixed land use in urban areas is as follows:
(a) Recreational land use:

1. Recreational land use is a use of urban land for fulfilling the needs of entertainment of people.
2. Public parks, swimming pools, theatres, etc. are included in recreational land use.

(b) Mixed land use:

1. Mixed land use is a use of urban land for fulfilling more than one wants at a time.
2. For example, area used for residential and entertainment purposes.

Question F.
Write about the features of planned cities.
Answer:
The features of planned cities are as follows:
(a) Need:

1. After industrial revolution, unplanned urbanisation occurred on a large scale all over the world.
2. Due to unplanned urbanisation, cities began to develop in a very haphazard manner.
3. People started migrating to cities in search of employment opportunities.

(b) Nature: City which is developed as per the pre-determined and planned layout of land use is called planned city.

(c) Singapore, Seoul from South Korea, Zurich from Switzerland, Washington D.C. from U.S.A., Brasilia from Brazil, Chandigarh, Bhubaneshwar from India are the examples of planned cities.

Question G.
Give information about 7/12 extract.
Answer:
The information about 7/12 extract is as follows:

1. 7/12 is an extract published and given by public revenue department of the government.
2. 7/12 extract gives detailed information of a particular registered land.
3. The register of the revenue department keeps a record of details of ownership rights of family, status of debt and loans, transfer of ownership, areas under different crops etc. related to registered land.
4. Village form no. 7 and Village form no. 12 are combined and 7/12 extract is prepared.
5. These village forms are available with the talathi of every village.
6. The accurate reading of 7/12 extract gives exact idea about ownership of land, tax levied on land, status of loan taken, etc.

Study the following map/figure/graph and answer the following questions:

Can you tell?

Study the Figure and answer the following questions:

Question A.
In which country is the land under forests more?
Answer:
The land under forests is more in Japan.

Question B.
In which country is the land under agriculture more?
Answer:
The land under agriculture is more in India.

Question C.
Considering the two questions above, how will you relate the physiography and climate of India and Japan with their respective land uses?
Answer:
Due to plains and monsoon climatic conditions, the population in India is more. Therefore, agricultural land use is prominent in India. Due to mountainous region and more proportion of precipitation, the forest land use is prominent in Japan.

Question D.
Correlate their land use and development.
Answer:
The land use in India shows comparatively low development. On the other hand, land use in Japan shows comparatively high development.

Question E.
Which land use is found in Japan?
Answer:
The land use like agricultural land use, forest land use, grassland land use, other land use, etc. are found in Japan.

Question F.
Considering the land use in both the countries, make a list of factors affecting land use.
Answer:
Considering the land use in both the countries, lists of factors affecting land use are as follows:
(a) Factors affecting land use in India:

1. Fertility of soil
2. Climatic conditions
3. Natural resources
4. Slope of land, etc.

(b) Factors affecting land use in Japan:

1. Technical advancement
2. Availability of resources
3. Government policies, etc.

Can you tell?

Study the Figure and answer the following questions:

Question A.
What kind of land use is shown in Figure 6.2 and 6.3?
Answer:
Land use shown in Figure 6.2 is agricultural land use and land use shown in Figure 6.3 is non-agricultural land use.

Question B.
Can you tell in which area the property is located?
Answer:
The property shown in Figure 6.2 is located in rural areas and the property shown in Figure 6.3 is located in urban areas.

Can you tell?

Study the Figure and answer the following questions:

Question A.
Which are the land uses of 1990-91 that show decline in 2010-11? What could be reasons for this?
Answer:
Total agricultural land use and other non-agricultural land use of 1990-91 show decline in 2010-11. Increased urbanisation could be reason for this.

Question B.
Which type of land use is the maximum? What would be the impact of this on India’s environment?
Answer:
Agricultural land use is the maximum. It indicates that India is an agrarian country and its environment is comparatively more natural.

Question C.
Can a decline in the area under agriculture equated with food shortage?
Answer:
A decline in the area under agriculture cannot be equated with food shortage. With modern technology, the maximum agricultural food production can be undertaken in limited areas.

Can you tell?

Study the figure and answer the following questions:

Question A.
What is the percentage of land suitable for cultivation?
Answer:
The percentage of land suitable for cultivation is 56.8.

Question B.
What is the percentage of barren land?
Answer:
The percentage of barren land is 8.3.

Question C.
What is the percentage of land under forest in Maharashtra?
Answer:
The percentage of land under forest in Maharashtra is 16.9.

Question D.
What is the percentage of non- agricultural land in Maharashtra?
Answer:
The percentage of non-agricultural land in Maharashtra is 10.2.

Give it a try.

Study the Figure. It shows the satellite images of Mondha Village (Taluka – Hingna, District – Nagpur).

Question A.
Find out the changes in land use pattern over time and write a note.
Answer:

1. The satellite image of Mondha Village in Hingna taluka in Nagpur district shows that agricultural land use in the village has declined from 2010 to 2017.
2. The satellite image of Mondha Village in Hingna taluka in Nagpur district shows that residential land use in the village has increased from 2010 to 2017.
3. Urbanisation, increasing population, etc. factors must be responsible for changes in land use pattern over time in Mondha Village.

Thought Provoking Question:

Think about it.

Question A.
If land is left fallow, or is not in use, then can it be termed as a kind of land use?
Answer:
1. The agricultural land which is temporarily not in use is called fallow land.
2. Fallow land use is a form of rural land use.
3. To increase the fertility of soil, farmers do not use a part of agricultural land for few seasons. After one or two seasons fallow land is again utilized for cultivation. Therefore, if land is left fallow, or is not in use, then it can be termed as a kind of land use.

Open-Ended Question:

Question A.
Write the advantages of planned cities in your own words.
Answer:
The advantages of planned cities are as follows:

1. There will not be a problem of traffic jam in planned cities.
2. The level of pollution will be the minimum in the planned cities.
3. The planned cities will be clean and they will maintain environmental balance.
4. The quality of human life will be superior in planned cities.

Balbharti Maharashtra State Board Class 8 Geography Solutions Chapter 2 Interior of the Earth Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Geography Solutions Chapter 2 Interior of the Earth

Class 8 Geography Chapter 2 Interior of the Earth Textbook Questions and Answers

1. Tick [✓] the correct options in the box:

Question A.
There are two layers in the crust.
(a) Inner and outer crust [ ]
(b) Continental and oceanic crust [ ]
(c) Surface and oceanic crust [ ]
(d) Mantle and core [ ]
Answer:
(b) Continental and oceanic crust [✓]

Question B.
Which element is found in both mantle and crust?
(a) Silica [ ]
(b) Magnesium [ ]
(c) Aluminium [ ]
(d) Iron [ ]
Answer:
(b) Magnesium [✓]

Question C.
Which of these minerals are found in the core of the earth?
(a) Iron – magnesium [ ]
(b) Magnesium – nickel [ ]
(c) Aluminium – iron [ ]
(d) Iron – nickel [ ]
Answer:
(d) Iron – nickel [✓]

Question D.
The inner core is in which state?
(a) Gaseous [ ]
(b) Solid [ ]
(c) Liquid [ ]
(d) Semi-solid [ ]
Answer:
(a) Gaseous [✓]

Question E.
The outer core is made up of
(a) Iron [ ]
(b) Gold [ ]
(c) Hydrogen [ ]
(d) Oxygen [ ]
Answer:
(a) Iron [✓]

Question F.
The layer of the earth on which we live…
(a) Mantle [ ]
(b) Core [ ]
(c) Crust [ ]
(d) Continental crust [ ]
Answer:
(d) Continental crust [✓]

2. Tell whether right or wrong. Correct the wrong statement

Question A.
The density of various materials is not the same in the interior of the earth.
Answer:
Correct.

Question B.
The core of the earth’s interior is made up of hard rocks.
Answer:
Incorrect.
Correct statement: The core of the earth’s interior is made up of elements, viz. iron and nickel.

Question C.
Secondary waves cannot pass through outer core.
Answer:
Correct.

Question D.
Continental crust is made up of silica and magnesium.
Answer:
Incorrect.
Correct statement: Continental crust is made up of silica and aluminum.

3. Answer the following

Question A.
What are the two parts of the crust? What is the basis of classification?
Answer:

1. Continental crust and the Oceanic crust are the two parts of the crust.
2. The crust is classified on the basis of whether it lies below the land or the ocean.
3. The part of the crust lying below the continent is known as the continental crust.
4. The part of the crust lying below the ocean is known as the oceanic crust.

Question B.
Why is the upper layer of the mantle known as the asthenosphere?
Answer:

1. The upper layer of the mantle is in liquid state.
2. The rocks in the upper 100 to 200 km of the mantle melt due to the heat and magma is created. Magma chambers are found in this layer of the earth.
3. Due to the heat and pressure, the energy waves are created in mantle. These energy waves move in vertical direction and magma comes out on the surface of the earth by volcanic eruptions.
4. These endogenitic movements continuously occur in the upper layer of the mantle. Therefore, the upper layer of the mantle is known as the asthenosphere.

Question C.
Magnetosphere of the earth is a result of rotation. Explain.
Answer:
1. The average temperature of the outer core of the earth is around 5000° C. The average temperature of the inner core of the earth is around 6000° C. This difference between the temperature results in formation of vertical currents.

2. The rotation of the earth gives eddy (circular) motion to these currents.

3. Electric currents develop in these spiral eddies of liquid iron leading to generation of the magnetic field of the earth. This magnetic field is called magnetosphere. In this way, the magnetosphere is formed due to the rotation of the earth.

4 Draw neat diagrams. label them and explain.

Question A.
The interior of the earth
Answer:

Explanation:

1. Inner Core: It is the center and the hottest layer of the Earth. The inner core is solid and made up of iron and nickel.
2. Outer Core: The outer core of the Earth is similar to a very hot ball of metals. It is composed of metals such as iron and nickel. The outer core surrounds the inner core.
3. Mantle: Mantle is the widest section of the Earth. Mantle is mainly made up of semi-molten rock known as magma. The rock is hard in the upper part of the mantle, but lower down the rock is softer and begins to melt. The mantle consists of very hot and dense rock.
4. Crust: The crust is the outer layer where we live. It’s a solid rock layer divided into two types: Continental crust covers the land and Oceanic crust covers water.

Question B.
Magnetic pole and equator
Answer:

5. Give geographical reasons:

Question A.
There are discontinuities in the interior of the earth.
Answer:
1. There is a difference between the elements, temperatures and the pressure found in the three parts of the interior of the earth, viz, crust, mantle and core.

2. In the interiors of the earth, the transitional areas are found between (a) continental crust and oceanic crust (b) crust and mantle (c) upper mantle and lower mantle (d) mantle and core and (e) outer core and inner core. Therefore, there are discontinuities in the interior of the earth.

Question B.
There is correlation between the density of metals and their location in the interior of the earth.
Answer:
1. The rocks found in the crust have predominance of the compounds of silicon, aluminium, magnesium, etc. These compounds are lighter in weight. Therefore, they are found in the upper layer of the interior of the earth.

2. The elements like iron, nickel are found in the core of the earth. These elements are heavier in weight. Thus, metals with low density are found in upper level in the interior of the earth and the metals with high density are found in the lower level in the interior of the earth. Thus, there is correlation between the density of metals and their location in the interior of the earth.

Question C.
Mantle is the centre of earthquake and volcanic eruptions.
Answer:
1. The rocks in the upper 100 to 200 km of the mantle melt due to the heat and the magma is created.
2. Magma chambers are found in this layer of the earth.

3. Due to the heat and pressure, the energy waves are created in mantle. These energy waves move in vertical direction and magma comes out on the surface of the earth by volcanic eruptions. Thus, mantle is the centre of earthquake and volcanic eruptions.

Question D.
The thickness of the crust below the continents is more as compared to oceans.
Answer:
1. The density of the crust below the continents is 2.65 to 2.90 gm/cm³ The density of the crust below the oceans is 2.90 to 3.3 gm/cm³

2. As the density of the crust below the continents is comparatively low, it keeps floating on the mantle. It does not subduct into mantle. As its effect, the thickness of the crust below the continents is found to be high.

3. As the density of the crust below the ocean is comparatively high, it subducts into mantle leading to its low thickness. Thus, the thickness of the crust below the continents is more as compared to oceans.

Question E.
Earth is protected because of the magnetosphere.
Answer:

1. The ozone layer protects the earth from ultraviolet radiation.
2. The earth’s magnetosphere serves to deflect most of the solar wind, whose charged particles would otherwise strip away the ozone layer. In this way, the earth is protected because of the magnetosphere.

Know this too:

1. The average density of the earth is 5.5 gm/cm³.
2. The rocks in the upper 100 to 200 km of. the mantle melt due to heat.
3. The mixture of molten rocks, volatiles, etc. found beneath the surface of the earth is called magma.
4. The mixture of molten rocks, volatiles, etc. erupted from volcano or fissure on the surface of the earth is called lava.

Activity:

Question 1.
Prepare a model of the earth’s interior.
Answer:

1. The density of the earth goes on increasing from its surface to the centre.
2. The average density of the crust of the earth is approximately 2.98 gm/cm³.
3. The average density of the mantle of the earth is approximately 5.7gm/cm³.
4. The average density of the outer core of the earth is approximately 9.8 gm/cm³.
5. The density of the inner core at the centre of the earth is approximately 13 gm/cm³.

Class 8 Geography Chapter 2 Interior of the Earth Additional Important Questions and Answers

Tick [✓] the correct options in the box:

Question A.
Which seismic waves can travel through liquid medium?
(a) Primary waves [ ]
(b) Secondary waves [ ]
(c) Surface waves [ ]
(d) Oceanic waves [ ]
Answer:
(a) Primary waves [✓]

Question B.
Which of the following layers of the earth has the highest density?
(a) Crust [ ]
(b) Mantle [ ]
(c) Outer core [ ]
(d) Inner core [ ]
Answer:
(d) Inner core [✓]

Question C.
Which of the following waves can travel through all the layers of the interior of the earth?
(a) Primary [ ]
(b) Secondary [ ]
(c) Tertiary [ ]
(d) Surface [ ]
Answer:
(a) Primary [✓]

Question D.
Which of the following layers of the interior of the earth is in solid form and cool?
(a) Crust [ ]
(b) Mantle [ ]
(C) Outer core [ ]
(d) Inner core [ ]
Answer:
(a) Crust [✓]

Examine the statements and incorrect ones :

Question A.
As we move deeper the surface, temperature keeps decreasing.
Answer:
Incorrect.
Correct statement: As we move deeper the surface, temperature keeps increasing.

Question B.
Magma chambers are found in lower mantle.
Answer:
Incorrect.
Correct statement: Magma chambers are found in upper mantle.

Question C.
The discontinuity is found between the crust, mantle and core.
Answer:
Correct.

Answer the following questions in one sentence each:

Question A.
In which of the layers of the interior of the earth is magma formed?
Answer:
Magma is formed in the mantle (upper mantle) of the earth.

Question B.
What are the two parts of the core?
Answer:
Outer core and inner core are the two parts of the core.

Match the columns and complete the chain :

Question A.

‘A’ Column (The layer of the interior of the earth)	‘B’ Column (Density)	‘C’ Column (Elements found)
1. Sial	(i) 13.3 gm/cm3	(a) Silica and Magnesium
2. Sima	(ii) 2.65 to 2.90 gm/cm3	(b) Nickel and Iron
3. Inner core	(iii) 2.90 to 3.3 gm/cm3	(c) Silica and Aluminium

Answer:

‘A’ Column (The layer of the interior of the earth)	‘B’ Column (Density)	‘C’ Column (Elements found)
1. Sial	(ii) 2.65 to 2.90 gm/cm3	(c) Silica and Aluminium
2. Sima	(iii) 2.90 to 3.3 gm/cm3	(a) Silica and Magnesium
3. Inner core	(i) 13.3 gm/cm3	(b) Nickel and Iron

Answer the following questions in brief:

Question A.
Describe the changes that take place in the temperatures from the surface of the earth to its centre.
Answer:

1. The process of cooling of the earth started from the surface. The temperature goes on increasing from the surface towards the core.
2. The surface of the earth is cool and solid.
3. The centre of the earth is extremely hot. The temperature at the centre of the earth is around 5500° to 6000° C.

Question B.
Describe the changes that take place in the density of the earth from its surface to the centre.
Answer:

1. The density of the earth goes on increasing from its surface to the centre.
2. The average density of the crust of the earth is approximately 2.98 gm/cm³.
3. The average density of the mantle of the earth is approximately 5.7gm/cm³.
4. The average density of the outer core of the earth is approximately 9.8 gm/cm³.
5. The density of the inner core at the centre of the earth is approximately 13 gm/cm³.

Question C.
Write in brief about the travelling of various types of earthquake waves through the layers of interior of the earth.
Answer:

1. The primary earthquake waves travel through the mantle as well as the core of the earth.
2. While travelling through the core of the earth, the direction of the primary earthquake waves gets altered.
3. While travelling through the core, the speed of the primary earthquake waves decreases.
4. The secondary earthquake waves can travel only through the mantle of the earth. These waves get absorbed in the core of the earth. Thus, these waves cannot travel through the core of the earth.

Write short notes on the following:

Question A.
The crust.
Answer:
1. The uppermost layer of the interior of the earth is called the crust. Continental crust and the oceanic crust are the two parts of the crust.

2.The thickness of the continental crust is approximately 16 km to 45 km. On the other hand, the thickness of the oceanic crust is approximately 7 km to 10 km

3. The density of the continental crust is approximately 2.65 to 2.90 gm/cm. On the other hand, the density of the oceanic crust is approximately 2.65 to 2.90 gm/cm³.

4. Silica and aluminium are the main elements found in the continental crust. Therefore, it is also called Sial. On the other hand, Silica and Magnesium are the main elements found in the oceanic crust. Therefore, it is also called Sima.

Question B.
The mantle.
Answer:
1. The mantle is located below the crust of the earth. The mantle is divided into the upper mantle and the lower mantle.

2. The thickness of the mantle is approximately 2870 km. The average density of mantle is approximately 4.5 gm/cm³.

3. The rocks in the upper 100 to 200 km of the mantle melt due to the heat and magma is created. Magma chambers are found in this layer of the earth. Due to the heat and pressure, the energy waves are created in mantle. These energy waves move in vertical direction and magma comes out on the surface of the earth by volcanic eruptions.

4. These endogenitic movements continuously occur in the upper layer of the mantle. Therefore, the upper layer of the mantle is known as the asthenosphere.

5. The average thickness of mantle is approximately 2870 km. Its average density is approximately 4.5 gm/cm³. The temperature at the depth of 2400 to 2900 km is around 2200° to 2500° C. The density of the lower mantle is approximately 5.7 gm / cm³.

Question B.
The outer core.
Answer:
1. The outer core is located below the lower mantle.
2. It is located at the depth from 2900 km to 5100 km from the surface of the earth.
3. The average temperature of the outer core of the earth is around 5000° C. The density of the outer core of the earth is approximately 9.8 gm/cm.

4. The secondary earthquake waves cannot travel from the core of the earth. Therefore, it is inferred that the outer core of the earth must be in liquid or semi-liquid form. The primary earthquake waves can travel from the outer core of the earth.
5. The vertical currents originate in the outer core of the earth.

Question C.
The inner core.
Answer:

1. The inner core is located below the upper core.
2. It is located at the depth from 5150 km to 6371 km from the surface of the earth.
3. The average temperature of the inner core of the earth is around 6000° C. The density of the inner core of the earth is approximately 13.3 gm/cm³.
4. The elements, viz. Iron (Ferrous) and Nickel (Ni) are mainly found in the inner core of the earth. Therefore, it is also called Nife.
5. The temperature at the centre of the earth is almost equivalent to the surface temperature of the sun.

Give geographical reasons for the following:

Question A.
The secondary waves of earthquake cannot travel through the core of the earth.
Answer:

1. The secondary waves of earthquake can travel only through the solid state of the interior of the earth.
2. The outer core of the centre of the earth is in liquid state. Therefore, the secondary waves of earthquake cannot travel through the core of the earth.

Question B.
The inner core is called Nife.
Answer:

1. The inner core predominantly comprises iron and nickel.
2. The word Nife is derived from the word Nickel (Ni) and Iron (Ferrous) (Fe). Therefore, the inner core is called (Ni + Fe) Nife.

Question C.
The upper layer of the crust is called Sial.
Answer:

1. The rocks in the upper layer of the crust have predominance of the compounds of silicon and aluminium.
2. The word Sial is derived from the word Silica (Si) and Aluminium (Al). Therefore, the upper layer of the crust is called (Si + Al) Sial.

Question D.
The lower layer of the crust is called Sima.
Answer:

1. The rocks in the lower layer of the crust have predominance of the compounds of silicon and magnesium.
2. The word Sima is derived from the word Silica (Si) and Magnesium. (Ma). Therefore, the lower layer of the crust is called (Si + Ma) Sima.

Study the following map/ figure /graph and answer the following questions : 

Question A.
At what depth does the curve of the secondary waves seem to have ended in figure (A)?
Answer:
The curve of the secondary waves seems to have ended around the depth of 2900 km in figure (A).

Question B.
What is the velocity of the secondary waves around the boundary of the outer core shown in figure (A)?
Answer:
The velocity of the secondary waves is 6 to 8 km/sec around the boundary of the outer core shown in figure (A).

Question C.
What conclusion can be drawn on the basis of the curve of the secondary waves stopping around the depth of 2900 km?
Answer:
On the basis of the curve of the secondary waves stopping around the depth of2900 km, it can be concluded that secondary waves do not enter the core.

Question D.
What is the velocity of the primary waves at the time of entering the outer core shown in figure (A)?
Answer:
The velocity of the primary waves at the time of entering the outer core shown in figure (A) is 8 km/sec.

Question E.
What conclusions can be drawn about the intensity of the gravitational force shown in Figure (B)?
Answer:
The following conclusions can be drawn about the intensity of the gravitational force shown in Figure (B):

1. Gravitational force increases at certain depth from the surface of the earth and then it reduces according to the depth.
2. At the centre of the earth, the gravitational force is zero.

Thought-Provoking Question:

Think about it:

Question 1.
Imagine about the earth’s interior and- write 10-12 sentences on it.
Answer:

1. The interior of the earth will be very hot.
2. Huge sized rocks will be present I in the upper layers of the interior of the earth.
3. Due to extreme heat and pressure, the rocks must be melting in the interior of the earth.
4. Due to the melting of the rocks, magma will be created in the interior of the earth.
5. Due to endogenous movements in the interior of the earth, volcanic eruptions will occur on the surface of the earth.
6. The primary earthquake waves will be travelling through the mantle and the core of the earth.
7. The secondary earthquake waves will be travelling only through the mantle of the earth.
8. The temperature in the interior of the earth will get increased with the depth.
9. The highest temperature will be found at the centre of the earth.
10. The elements like silica, aluminium, magnesium, iron and nickel will be found in the various layers of the interior of the earth.

Open-Ended Question:

Question A.
What precautions can be taken to reduce the damage caused by earthquakes?
Answer:
The following precautions can be taken to reduce the damage caused by earthquakes:

1. Taking cover under a desk or a table or sturdy piece of furniture to protect oneself.
2. Finding clear spot away from buildings, trees and power lines. Dropping to the ground and staying there until the shaking stops.
3. Switching off the power supply, gas in-home/office, etc.
4. Helping the victims at the earliest.

Balbharti Maharashtra State Board Class 8 Geography Solutions Chapter 4 Structure of Ocean Floor Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Geography Solutions Chapter 4 Structure of Ocean Floor

Class 8 Geography Chapter 4 Structure of Ocean Floor Textbook Questions and Answers

1. Choose the correct option:

Question a.
Like there are landforms on land, ocean floor also has submerged landforms because ………….
(i) there is land under water
(ii) there are volcanoes under water
(iii) land is continuous and there is water in deeper parts
(iv) though land is continuous, its level is not the same everywhere like that of water
Answer:
(iv) though land is continuous, its level is not the same everywhere like that of water

Question b.
Which part of the ocean floor is most useful to the man?
(i) Continental shelf
(ii) Continental slope
(iii) Abyssal plains
(iv) Marine deeps
Answer:
(i) Continental shelf

Question c.
Which one of the following option is related to marine deposits?
(i) Rivers, glaciers, continental shelf, remains of plants and animals
(ii) Volcanic ash, continental shelf, remains of plants and animals
(iii) Volcanic ash, lava, fine particles of soil
(iv) Volcanic ash, remains of plants and animals, abyssal plants
Answer:
(iii) Volcanic ash, lava, fine particles of soil

2. Question a.
Name the landforms shown in the following figure.
(Note: The answer is given directly.)

Answer:

Question b.
Which of these landforms are useful for deep sea research?
Answer:
Submarine plateau and marine trench are the landforms useful for deep sea research.

Question c.
Which of these are appropriate to be used for the protection of marine borders and naval base building?
Answer:
Continental shelf is appropriate to be used for the protection of marine borders and naval base building.

3. Give geographical reasons:

Question a.
The study of ocean floor is useful to man.
Answer:

1. Various minerals, rocks, fine I soil particles are found on the sea floor.
2. Remains of marine plants and animals are also found on the ocean floor.
3. To study the marine life, mineral wealth as well as the process of volcanic eruption, the study of ocean floor is useful to man. ‘

Question b.
The continental shelf is a paradise for fishing activity.
Answer:

1. Being a shallowest part of the ocean bed, sunlight reaches up to continental shelf easily.
2. As its effect, algae, plankton, etc. grows on a large scale on continental shelf.
3. Algae, plankton, etc. is food for fish. Therefore, fish are found on a large scale on continental shelf. Therefore, the continental shelf is paradise for fishing activity.

Question c.
Some marine islands are actually the peaks of sea mountains.
Answer:

1. The hundreds of kilometres wide and thousands of kilometres long hills found on the ocean bed are called submerged hills.
2. Peaks of some of the submerged hills come above the sea level.
3. These peaks are the visible land areas surrounded from all sides by water. These peaks are called islands. Thus, some marine islands are actually the peaks of sea mountains.

Question d.
The continental slope is considered to be the boundary of continents.
Answer:

1. Continental slope lies beyond the continental shelf.
2. The deep abyssal plain begins beyond the continental slope. Therefore, the continental slope is considered to be the boundary of continents.

Question e.
The disposal of waste materials in the oceans by man is harmful to the 1 environment.
Answer:

1. The disposal of waste materials in the oceans by man increases the pollution of sea water.
2. This disposed waste materials harm the life of marine animal life and marine plant. Thus, the disposal of waste materials in the oceans by man is harmful to the environment.

4. Observe the map on Pg 27 in ‘Give it a try’ and answer the following questions:

Question a.
Madagascar and Sri Lanka are related to which landform of the ocean floor?
Answer:
Madagascar and Sri Lanka are related to island of the ocean floor.

Question b.
Near which continent are these landforms located?
Answer:
Madagascar is located near the continent of Africa and Sri Lanka is located near the continent of Asia.

Question c.
Which islands in our country are examples of peaks of submerged mountains?
Answer:
Andaman and Nicobar islands in our country are examples of peaks of submerged mountains.

Activity:

Question a.
prepare a model of the ocean floor.
Answer:

1. While studying the ocean floor, we must keep in mind the age of the ocean bed. By studying the deposits on the ocean bed, it occurred to the scientists that the deposits at the ocean floor are not older than 200 million years.

2. The maximum age of the rocks on the continents is supposed to be 3200 million years. Then where have the deposits on the sea bed which are older than 200 million years gone? This made the scientists restless. Then they started the study of the rocks along with the deposits.

3. This made them realize that the rocks are also not older than 200 million years. It was inferred that the ocean floor is very young as compared to the earth’s surface. Now this is unanimously accepted. This research was then used in the study of the concept of plate tectonics.

Class 8 Geography Chapter 4 Structure of Ocean Floor Additional Important Questions and Answers

Choose the correct answer and complete the sentences:

Question a.
Continental slope has slope.
(a) flatter
(b) broader
(c) steeper
(d) lower
Answer:
(c) steeper

Question b.
The average depth of the oceans is around metres.
(a) 7300
(b) 3700
(c) 3900
(d) 3300
Answer:
(b) 3700

Examine the following statements and correct the incorrect ones:

Question a.
Abyssal plain lies beyond the continental shelf.
Answer:
Incorrect.
Correct statement: Abyssal plain lies beyond the continental slope.

Question b.
Around 51 per cent of the surface of the earth is covered by water.
Answer:
Incorrect.
Correct statement: Around 71 per cent of the surface of the earth is covered by water.

Question c.
Natural gas and mineral oil can be obtained from the continental shelf.
Answer:
Correct.

Question d.
For survey purpose in India, the height of sea level at Kanyakumari is considered to be zero.
Answer:
Incorrect.
Correct statement: For survey purpose in India, the height of sea level at Chennai is considered to be zero.

Question e.
Active volcanoes are mostly seen in marine trenches.
Answer:
Correct.

Answer the following questions in one sentence each:

Question a.
What is called continental shelf?
Answer:
The land near the coast and submerged under the sea is called continental shelf.

Question b.
What is called continental slope?
Answer:
The steeper slope of the sea bed beyond the extent of continental shelf is called continental slope.

Question c.
What is called abyssal plain?
Answer:
The flat part of the sea bed that lies
beyond the continental slope is called abyssal plain.

Question d.
What is called submerged hills?
Answer:
The hundreds of kilometres wide and thousands of kilometres long hills found on the ocean bed are called submerged hills.

Question e.
What is called marine islands?
Answer:
Peaks of some of the submerged hills that come above the sea level are called marine islands.

Question f.
What is called submarine plateau?
Answer:
The flat and extensive summit of marine island is called submarine plateau.

Question g.
What is called marine deep?
Answer:
The landforms on the ocean bed that are comparatively less extending and shallower ones are called marine deep.

Question h.
What is called marine trench?
Answer:
The landforms on the ocean bed that are comparatively more extending and deeper ones are called marine trench.

Match the columns and complete the chain:

Question a.

‘A’ Column	‘B’ Column	‘C’ Column
1. Andaman – Nicobar	(i) Submarine plateau	(a) Pacific Ocean
2. Chagos	(ii) Located on continental shelf	(b) Bay of Bengal
3. Mariana	(iii) Islands	(c) Arabian Sea
4. Mumbai High	(iv) Marine deep	(d) Indian Ocean

Answer:

‘A’ Column	‘B’ Column	‘C’ Column
1. Andaman – Nicobar	(iii) Islands	(b) Bay of Bengal
2. Chagos	(i) Submarine plateau	(d) Indian Ocean
3. Mariana	(iv) Marine deep	(a) Pacific Ocean
4. Mumbai High	(ii) Located on continental shelf	(c) Arabian Sea

Answer the following questions in brief:

Question a.
What is marine deposits?
Answer:

1. Marine deposit is a type of marine deposition.
2. The rivers and glaciers flowing from the continent bring pebbles, clay, soil, etc. with them when they meet sea or ocean.
3. These materials get deposited on the continental shelf. The deposits are known as marine deposits.
4. Due to pressure of sea water and deposition of layers over layers of sediments, sedimentary rocks are formed.
5. Marine life and the availability of minerals in the sea bed can be studied with the help of marine deposits.

Question b.
What is marine oozes?
Answer:

1. Marine oozes is a type of marine deposit.
2. Lava and ash erupting out of volcano, fine soil particles, remains of plants and animals, etc. get deposited on marine abyssal plains. Deposits of these materials on the abyssal plains are known as marine oozes.
3. Marine oozes are in the form of fine clay. The percentage of remains of plants and animals in marine oozes is up to 30 per cent.
4. Marine oozes are also useful to study marine life and the availability of minerals in the sea bed.

Question c.
Write in brief about the continental shelf.
Answer:
1. The land near the seacoast and submerged under the sea is called continental shelf. The depth of continental shelf is about 200 metres below the sea level.

2. Continental shelf is found to be narrow along the coasts of some continents and broad along the coasts of some other continents.

3. Being a shallowest part of the ocean bed, sunlight reaches up to continental shelf easily. As its effect, the food for fish like algae, plankton, etc. grows on a large scale on continental shelf. Therefore, continental shelf is useful for fishing occupation.

4. Various minerals, natural gas and mineral oil, etc. can also be obtained from mining the continental shelf. For example, Mumbai High located on the continental shelf of the Arabian Sea is a source from where the mineral oil and natural gas is obtained.

Question d.
Write in brief about the continental slope.
Answer:

1. The steep slope of the sea bed beyond the extent of continental shelf is called continental slope.
2. The depth of the continental slope is from 200 metres to 3600 metres below the sea level.
3. The continental slope is found to be comparatively narrower.
4. The lower boundary of the continental slope is considered as the boundary of I continent.

Question f.
Write in brief about the abyssal plains.
Answer:

1. The flat part of the sea bed that lies beyond the continental slope is called abyssal plains.
2. Various submerged landforms like
   submerged hills, submerged mountains, etc. are seen on abyssal plains.
3. Submarine plateaus are also found on the abyssal plains.

Question g.
Write in brief about mean sea level.
Answer:

1. The average of the highest high tide and the lowest low tide is considered to calculate the mean sea level.
2. This average is considered to be zero sea level.
3. The altitude of any place above the sea level is measured and expressed in positive value. (For example, Mount Everest is 8848 metres high.)
4. The depth of any place below the sea level is measured and expressed in negative value. (For example, Mariana Trench is 11034 metres below sea level.)

Study the following map/figure/graph and answer the following questions:

Can you tell?

Question a.
What parameters were used for classifying the landforms on the earth?
Answer:
Altitude and the shape of the land were the parameters used for classifying the landforms on the earth.

Question b.
What parameters were used for naming the landforms below water?
Answer:
Depth from the seafloor and the shape of the land were the parameters used for naming the landforms below water.

Give it a try.

Question a.
Name the submerged landforms shown in the diagram.
(Note: The answer is given directly.)

Answer:

Question b.
Identify the ocean shown in the map of the ocean floor.
Answer:
The ocean shown in the map of the ocean floor is Indian Ocean.

Question c.
Which region would be ideal for fishing and why?
Answer:
The region near Madagascar island would be ideal for fishing. Madagascar island has a shallow continental shelf. The warm stream and cold stream also meet near Madagascar island. Therefore, the region near Madagascar island would be ideal for fishing.

2. Name the landforms shown in the following figure and answer the following questions:
(Note: The answer is given directly.)

Question a.

Answer:

Thought-Provoking Questions

Think about it.

Question a.
If the classification of landforms on land can be done on the basis of altitude and size, then how can the landforms submerged underwater are classified?
Answer:
If the classification of landforms on land can be done on the basis of altitude and size, then the landforms submerged underwater are classified on the basis of the depth from the seafloor and the shape of the land there.

Use your brainpower!

Do this activity when you go to the seashore with your parents or teachers. Observe the materials which have come with the waves. Classify them as per the flowchart given below:

Question a.
Which of these are perishable items?
Answer:
Plants, conches and shells, aquatic animals of these are perishable items.

Question b.
Which are non-perishable?
Answer:
Chemicals, metals and plastic/glass are non-perishable.

Question c.
What will happen because of perishable items?
Answer:
Perishable items will not create pollution of seacoast and seawater on a large scale. The remains of perishable items will get deposited in the form of marine oozes on the ocean bed.

Question d.
What will happen because of non-perishable items?
Answer:
Non-perishable items will create pollution of seacoast and seawater on a large scale.

Question f.
Suggest measures to control deposition of non-perishable items on the coast.
Answer:
The following measures can be taken to control deposition of non-perishable items on the coast:

1. Plastic bags, plastic or glass containers must be prohibited on the seacoasts.
2. Strict action must be taken against offenders carrying the banned products on the seacoasts.
3. Hoardings explaining the importance of clean seacoasts must be displayed on all the seacoast.

Question g.
How will you run a campaign of environmental conservation to keep the coasts clean?
Answer:
We will run a campaign of environmental conservation to keep the coasts clean as follows:

1. We will display hoardings explaining the importance of clean seacoasts on the seacoasts.
2. We will arrange street plays, dramas, etc. highlighting the importance of clean seacoasts.
3. We will arrange special programmes during the festivals like Ganeshotsav, Diwali, Christmas, etc. to keep the seacoasts clean.

Open-Ended Questions:

Question a.
Suggest measures to control deposition of non-perishable items on the coast.
Answer:
The following measures can be taken to control deposition of non-perishable items on the coast:

1. Plastic bags, plastic or glass containers must be prohibited on the seacoasts.
2. Strict action must be taken against offenders carrying the banned products on the seacoasts.
3. Hoardings explaining the importance of clean seacoasts must be displayed on all the seacoasts.

Question b.
How will you run a campaign of environmental conservation to keep the coasts clean?
Answer:
We will run a campaign of environmental conservation to keep the coasts clean as follows:

1. We will display hoardings explaining the importance of clean seacoasts on the seacoasts.
2. We will arrange street plays, dramas, etc. highlighting the importance of clean seacoasts.
3. We will arrange special programmes during the festivals like Ganeshotsav, Diwali, Christmas, etc. to keep the seacoasts clean.