# MCQ Questions for Class 11 Physics Chapter 13 Kinetic Theory with Answers

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## Kinetic Theory Class 11 MCQs Questions with Answers

Multiple Choice Type Questions

Question 1.
Which of the following can be the basis of sesparating a mixture of gases?
(a) Graham’s law of diffusion
(c) Charle’s law
(d) Boyle’s law

Answer: (a) Graham’s law of diffusion

Question 2.
In the equation, PV = RT, the V refers to the volume of:
(a) 1 g of a gas
(b) 1 mole of a gas
(c) 1 kg of gas
(d) any amount of gas

Answer: (b) 1 mole of a gas

Question 3.
Gases deviate from perfect gas behaviour because their molecules
(a) are polyatomic
(b) are of very small size
(c) don’t attract each other
(d) interact with each other through intermolecular forces

Answer: (d) interact with each other through intermolecular forces

Question 4.
Who gave the law of equipartition of energy?
(a) Maxwell
(b) Claussius
(c) Boltzmann
(d) Carnot

Question 5.
The law of equipartition of energy is applicable to the system whose constituents are:
(a) in orderly motion
(b) at rest
(c) in random motion
(d) moving with constant speed

Question 6.
The monoatomic molecules have only three degrees of freedom because they can possess
(a) only translatory motion
(b) only rotatory motion
(c) both translatory and rotatory motion
(d) translatory, rotatory and vibratory motion

Question 7.
A hotter gas implies higher average value of:
(a) heat content
(b) K.E.
(c) total energy
(d) internal energy

Question 8.
What is the number of degrees of freedom of an ideal diatomic molecule at ordinary temperature?
(a) 3
(b) 5
(c) 7
(d) 6

Question 9.
The number of degrees of freedom for translatory motion are
(a) dependent on the nature of translatory motion.
(b) same for all types of molecules.
(c) less for multiatomic molecules.
(d) more for multiatomic molecules.

Answer: (b) same for all types of molecules.

Question 10.
A man is climbing up a spiral type of staircase. His degrees of freedom are:
(a) 1
(b) 2
(c) 3
(d) more than 3

Question 11.
The energy associated with each degree of freedom of a gas molecule is
(a) zero
(b) $$\frac {1}{2}$$ kT
(c) kT
(d) $$\frac {3}{2}$$ kT

Answer: (b) $$\frac {1}{2}$$ kT

Question 12.
The mean K.E. of a monoatomic gas molecule is
(a) zero
(b) $$\frac {1}{2}$$kT
(c) kT
(d) $$\frac {3}{2}$$ kT

Answer: (d) $$\frac {3}{2}$$ kT

Question 13.
Equal volumes of two gases at the same temperature and pressure have the same
(a) number of molecules.
(b) r.m.s. velocity.
(c) no. of molecules with r.m.s. velocities.
(d) none of the above.

Question 14.
The absolute zero is that temperature at which
(а) all molecular linear velocities are zero.
(b) most of the molecular linear velocities are zero.
(c) most of the molecular linear velocities are not zero.
(d) the weight of the gas is zero.

Answer: (а) all molecular linear velocities are zero.

Question 15.
The speed of sound vs in a gas and rms speed of molecules are related as
(а) $$\frac {v_s}{v_rms}$$ = 1
(b) $$\frac {v_s}{v_rms}$$ = √γ
(c) $$\frac {v_s}{v_rms}$$ = $$\sqrt{\frac {3}{γ}}$$
(d) $$\frac {v_s}{v_rms}$$ = $$\sqrt{\frac {γ}{3}}$$

Answer: (d) $$\frac {v_s}{v_rms}$$ = $$\sqrt{\frac {γ}{3}}$$

Question 16.
Which of the following is not a postulate of kinetic theory of gases?
(a) The molecules of a gas are always at rest.
(b) The molecules of a gas are point masses.
(c) The molecules of a gas are perfectly elastic spheres.
(d) The molecules of a gas are identical.

Answer: (a) The molecules of a gas are always at rest.

Question 17.
The state of greatest potential energy is
(a) gaseous
(b) liquid
(c) solid
(d) solid as well as liquid

Question 18.
The volume of 5 moles of a gas at N.T.P. in litres is
(a) 112
(b) 11.2
(c) 1.12
(d) 1120

Question 19.
If r.m.s. speed of a gas increases, then its pressure :
(a) increases
(b) decreases
(c) remains same
(d) may increase or decrease

Question 20.
The pressure P and density p of a gas are related as
(a) P ∝ ρ
(b) P ∝ $$\frac {1}{ρ}$$
(c) P ∝ ρ²
(d) P ∝ $$\frac {1}{ρ^2}$$

Question 21.
What happens when the temperature of a gas contained in a vessel is raised?
(a) The molecules of gas move faster and pressure increases.
(b) The molecules of gas move faster and the pressure decreases
(c) The molecules of the gas move slower and the pressure, increases.
(d) The gas molecules move slower and the pressure decreases.

Answer: (a) The molecules of gas move faster and pressure increases.

Question 22.
For an ideal gas
(a) Size of molecules is negligible.
(b) There is no force of attraction or repulsion amongst the molecules.
(c) It strictly obeys the gas laws.
(d) All of the above.

Answer: (d) All of the above.

Question 23.
The r.m.s. velocity of a gas is
(a) directly proportional to the density of the gas.
(b) inversely proportional to the density of the gas.
(c) directly proportional to the square of density.
(d) inversely proportional to the square root of the density of the gas.

Answer: (d) inversely proportional to the square root of the density of the gas.

Question 24.
K.E. of gas molecules is zero at:
(a) 0°C
(b) 273°t
(c) -273°C
(d) none of the above

Question 25.
In kinetic theory’ of gases, it is assumed that:
(a) the collisions are not perfectly elastic.
(b) the molecular collisions change the density of the gas.
(c) the molecules don’t collide with each other on the well.
(d) between two collisions the molecules travel with uniform velocity.

Answer: (d) between two collisions the molecules travel with uniform velocity.

Fill in the blanks

Question 1.
The behaviour of real gases approximate to that of perfect gas at low ……………….. and high ………………..

Question 2.
Pressure exerted by an ideal gas is numerically equal to $$\frac {2}{3}$$rd of the mean kinetic energy per unit ……………….. of gas

Question 3.
The r.m.s. velocity of molecules at 0°C is doubled at ………………..

Question 4.
If the volume of a gas is reduced at constant temperature the frequency of collision ……………….. and mean free path ………………..

Question 5.
The ……………….. is the measure of average K.E. of the gas.

Question 6.
For a molecule having n degrees of freedom, the energy associated with the molecules is ………………..

Answer: $$\frac {n}{2}$$ kT

Question 7.
The K.E. of a body of mass m is E. The momentum of the body is ………………..

Answer: $$\sqrt {2mE}$$

Question 8.
One mole of every gas at ……………….. occupies the same volume Le. 22.4 litre.

Question 9.
The density of a gas ……………….. during collisions.

Question 10.
The number of molecules with higher most probable speed ……………….. with the rise in temperature.

Question 11.
Both STP or NTP refer to a temperature of ……………….. and ……………….. pressure.

Answer: 0°C or 273 K, 1 atm.

Question 12.
The volume of an ideal gas is ……………….. at absolute zero.

Question 13.
Temperature less than absolute zero is ………………..

Question 14.
Pressure of a gas ……………….. on increase of its temperature.

Question 15.
Pressure of a gas ……………….. on decrease of its volume.

Question 16.
Pressure of a gas increases on reducing volume due to ………………..

Answer: increase in the number of collisions per second.

Question 17.
Pressure of a gas increases on increasing its temperature due to ………………..

Answer: increase in velocity or K.E. of the gas molecules.

Question 18.
All molecular motions stop at ………………..

Question 19.
The temperature of a gas ……………….. when it is compressed.

Question 20.
Avogadro number is the number of molecules in ………………..

Answer: one mole of a gas

Question 21.
The pressure exerted by the molecules of a gas is due to ………………..

Question 22.
The perfect or ideal gas is one which obeys ………………..

Answer: Boyle’s law and Charle’s law.

Question 23.
The relation PV = RT can describe the behaviour of a real gas at ………………..

Answer: high temperature and low density or low pressure.

Question 24.
The quantity PV/kT represents ………………..

Answer: number of molecules in the gas.

Question 25.
On increasing the temperature of a gas from 27°C to 927°C, the r.m.s. speed is ………………..

Question 26.
The air of the atmosphere becomes cold at higher altitude because of ………………..

Question 27.
A perfect gas is one whose molecules don’t have ……………….. and the ……………….. is negligible as compared to the volume of the gas.

Answer: molecular attraction, volume of the molecules themselves.

Question 28.
K.E. of 1 mole of a gas is ………………..

Answer: $$\frac {3}{2}$$ RT.

Question 29.
K.E. of 1 molecule of a gas is ………………..

Answer: $$\frac {3}{2}$$ kT.

True/False Type Questions

1. Mark True/False statements
(a) The molecules of an ideal gas are point masses i.e. they are of negligible size.
(b) There is no force of attraction or repulsion amongst the molecules of an ideal gas.
(c) An ideal gas strictly obeys the gas laws.

(a) True
(b) True
(c) True.

2. Mark True/False statements
(a) The intermolecular force for an ideal gas is zero.
(b) The P.E. for the. molecules of an ideal gas is zero.
(c) The total energy of an ideal gas is purely due to kinetic energy of its molecules.

(a) True
(b) True
(c) True.

3. Mark True/False statements
(a) O2, N2, H2 gases are called permanent gases as they obey the gas laws.
(b) Real gases obey gas laws.
(c) The volume of an ideal gas at absolute zero becomes zero.

(a) True
(b) False
(c) True.

4. Mark True/False statements
(a) The molecules of all gases are identical.
(b) The molecules of the gases move randomly in all possible directions with all possible velocities.
(c) The molecules of a gas are perfectly elastic spheres.

(a) False
(b) True
(c) True.

5. Mark True/False statements
(a) The gas molecules move with a constant velocity along a straight line between two successive collisions.
(b) The density of the gas changes due to collisions.
(c) The no. of molecules having speeds tending to zero is very very small.

(a) True
(b) False
(c) True

6. Mark True/False statements
(a) The mean free path of the gas molecules increases with the increase in temperature.
(b) The average K.E. of one gram of all ideal gases at the same temperature is the same.

(a) True
(b) False.

7. Mark True/False statements
(a) The pressure of a gas increases with increase of temperature.
(b) Two different gases at the same temperature have equal root mean square velocities.

(a) True
(b) False

8. Mark True/False statements
(a) The pressure of a gas on the walls of the container increases as its volume is decreased at constant temperature.
(b) Absolute zero degree temperature is not the zero energy temperature.
(c) The mean free path increases with increase in temperature due to the increase in volume at constant pressure.

(a) True
(b) True
(c) True

9. Mark True/False statements
(a) The most probable speed increases with increase in temperature.
(b) The most probable speed is directly proportional to the square root of the absolute temperature.
(c) Absolute temperature can never be negative.

(a) True
(b) True
(c) True

10. Mark True/False statements
(a) The mean free path decreases with the increase in pressure at a constant temperature of the gas.
(b) The temperature of a gas in a container will increase when we put it on a moving train.
(c) Equal volumes of two gases at the same temperature and pressure have the same number of molecules.

(a) True
(b) False
(c) True

Match Type Questions

 Column I Column II (a) Obeys gas laws (i) zero (b) Volume of an ideal gas at absolute zero (ii) K.E. of gas molecules is zero (c) At absolute zero (iii) point masses (d) Molecules of an ideal gas (iv) mean free path (e) Distance covered by the molecules between two successive collisions (v) internal energy of a real gas (f) Depends on volume and temperature (vi) ideal gas (g) Number of molecules in one mole of a gas (vii) increases with the increase in temperature (h) Mean free path (viii) $$\frac {3}{2}$$ kT (i) K.E. per mole of a gas (ix) Avogadro’s number (j) K.E. per molecule of a gas (x) $$\frac {3}{2}$$ RT (k) Does not change during collisions (xi) density of gas
 Column I Column II (a) Obeys gas laws (vi) ideal gas (b) Volume of an ideal gas at absolute zero (i) zero (c) At absolute zero (ii) K.E. of gas molecules is zero (d) Molecules of an ideal gas (iii) point masses (e) Distance covered by the molecules between two successive collisions (iv) mean free path (f) Depends on volume and temperature (v) internal energy of a real gas (g) Number of molecules in one mole of a gas (ix) Avogadro’s number (h) Mean free path (vii) increases with the increase in temperature (i) K.E. per mole of a gas (x) $$\frac {3}{2}$$ RT (j) K.E. per molecule of a gas (viii) $$\frac {3}{2}$$ kT (k) Does not change during collisions (xi) density of gas