JEE Physics Kinetic Theory MCQS Set A

Question: Select the appropriate property of an ideal gas

• a) All of these
• b) It strictly obeys the ideal gas laws
• c) There are no forces of interaction between its molecules
• d) Its molecules are infinitesimally small

Answer: All of these

Question: A real gas behaves as an ideal gas at

• a) Very low pressure and high temperature
• b) High pressure and low temperature
• c) Low pressure and low temperature
• d) High pressure and high temperature

Answer: Very low pressure and high temperature

Question: A gas at a pressure P₀ is contained in a vessel. If the masses of all the molecules are halved and their velocities doubled, then the resulting pressure P will be

• a)

  

• b) P₀
• c) 2P₀
• d) 4P₀

Answer:

Question: If E is the energy density in an ideal gas, then the pressure of the ideal gas is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: A sample of gas in a box is at pressure P₀ and temperature T₀. If number of molecules is doubled and total kinetic energy of the gas is kept constant, then final temperature and pressure will be

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: By increasing temperature of a gas by 6°C its pressure increases by 0.4 %, at constant volume. Then initial temperature of gas is

• a) 1500 K
• b) 2000 K
• c) 750 K
• d) 1000 K

Answer: 1500 K

Question: Boyle’s law is obeyed by

• a) Ideal gas of constant mass and temperature
• b) Real gas of constant mass and temperature
• c) Both ideal and real gases at constant temperature and variable mass
• d) Both ideal and real gases of constant mass and variable temperature

Answer: Ideal gas of constant mass and temperature

Question: For an ideal gas the fractional change in its volume per degree rise in temperature at constant pressure is equal to [T is absolute temperature of gas]

• a) T^–1
• b) T²
• c) T³
• d) T⁰

Answer: T^–1

Question: The raise in the temperature of a given mass of an ideal gas at constant pressure and at temperature 27° to double its volume is

• a) 327°C
• b) 54°C
• c) 300°C
• d) 600°C

Answer: 327°C

Question: Which of the following methods will enable the volume of ideal gas to be increased four times?

• a) Double the temperature and reduce the pressure to half
• b) Double the temperature and also double the pressure
• c) Reduce the temperature to half and double the pressure
• d) Reduce the temperature to half and reduce the pressure to half

Answer: Double the temperature and reduce the pressure to half

Question: A container has N molecules at absolute temperature T. If the number of molecules is doubled but kinetic energy in the box remain the same as before, the absolute temperature of the gas is

• a)

  

• b) T
• c) 3T
• d) 4T

Answer: 3T

Question: During an experiment an ideal gas is found to obey an additional law VP2 = constant. The gas is initially at temperature T and volume V, when it expands to volume 2V, the resulting temperature is

• a)

  

• b)

  

• c)  2T
• d)

  

Answer:

Question: When pressure remaining constant, at what temperature will the r.m.s. speed of a gas molecules increase by 10% of the r.m.s. speed at NTP?

• a) 57.3ºC
• b) 557.3 K
• c) –57.3ºC
• d) 57.3 K

Answer: 57.3ºC

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: The average speed of gas molecules is v at pressure P. If by keeping temperature constant the pressure of gas is doubled, then average speed will become

• a) v
• b) 2v
• c)

  

• d)

  

Answer: v

Question:  Four molecules of a gas have speeds 1, 2, 3 and 4 km/s. The value of the r.m.s. speed of the gas molecules is

• a)

  

• b)

  

• c) 2.5 km/s
• d) None of these

Answer:

Question: The r.m.s. speed of the molecules of enclosed gas is V. What will be the r.m.s. speed if pressure is doubled keeping the temperature same?

• a) V
• b) 2V
• c) 4V
• d)

  

Answer: V

Question:  Four molecules of a gas have speeds 1, 2, 3 and 4 km/s. The value of the r.m.s. speed of the gas molecules is

• a) v
• b) 2v
• c)

  

• d) None of these

Answer: v

Question: The effect of temperature on Maxwell’s speed distribution is correctly shown by

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: Select the incorrect statement about Maxwell’s speed distribution

• a) The distribution curve is symmetric about the most probable speed
• b) The area under the distribution curve gives total number of molecules of the gas
• c) The distribution function depends only on the absolute temperature
• d) None of these

Answer: The distribution curve is symmetric about the most probable speed

More Questions........................................

Question: The ratio of number of collisions per second at the walls of containers by He and O₂ gas molecules kept at same volume and temperature, is (assume normal incidence on walls)

• a)

  

• b)

  

• c) 1 : 2
• d) 2 : 1

Answer:

Question: An ant is moving on a plane horizontal surface. The number of degrees of freedom of the ant will be

• a) 2
• b) 3
• c) 6
• d) 1

Answer:  2

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: Molar specific heat at constant volume, for a non-linear triatomic gas is (vibration mode neglected)

• a) 3R
• b) 4R
• c) 2R
• d) R

Answer: 3R

Question: A mixture of ideal gases has 2 moles of He, 4 moles of oxygen and 1 mole of ozone at absolute temperature T. The internal energy of mixture is

• a) 16 RT
• b) 14 RT
• c) 11 RT
• d) 13 RT

Answer: 16 RT

Question: E₀ and E_H respectively represents the average kinetic energy of a molecule of oxygen and hydrogen. If the two gases are at the same temperature, which of the following statement is true?

• a)

  

• b)

  

• c)

  

• d) Data insufficient

Answer:

Question: 14 g of CO at 27°C is mixed with 16 g of O₂ at 47°C. The temperature of mixture is (vibration mode neglected)

• a) 37°C
• b) 27°C
• c) 32°C
• d) –5°C

Answer: 37°C

Question:

• a) 1.50
• b) 1.6
• c) 1.40
• d) 1.33

Answer: 1.50

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: On increasing number density for a gas in a vessel, mean free path of a gas

• a) Decreases
• b) Increases
• c) Remains same
• d) Becomes double

Answer: Decreases

Question: At room temperature the rms speed of the molecules of a certain diatomic gas is found to be 1920 m/s. The gas is

• a) H₂
• b) F₂
• c) Cl₂
• d) O₂

Answer: H₂

Question: An ideal gas is enclosed in a container of volume V at a pressure P. It is being pumped out of the container by using a pump with stroke volume v. What is final pressure in container after n-stroke of the pump? (assume temperature remains same)

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: Variation of atmospheric pressure, with height from earth is

• a) Exponential
• b) Hyperbolic
• c) Parabolic
• d) Linear

Answer: Exponential

Question: A narrow glass tube, 80 cm long and opens at both ends, is half immersed in mercury, now the top of the tube is closed and is taken out of mercury. A column of mercury 20 cm long remains in the tube. Find atmospheric pressure

• a) 60 cm of Hg column
• b) 20 cm of Hg column
• c) 20 cm of air column
• d) 60 cm of air column

Answer: 60 cm of Hg column

Question: One mole of monatomic gas and three moles of diatomic gas are put together in a container. The molar specific heat (in JK^–1 mol^–1) at constant volume is (Let R = 8 JK^–1 mol^–1)

• a) 18
• b) 19
• c) 20
• d) 21

Answer: 18

Question: Two closed containers of equal volume filled with air at pressure P₀ and temperature T₀. Both are connected by a narrow tube. If one of the container is maintained at temperature T₀ and other at temperature T, then new pressure in the containers will be

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: The temperature of a gas is –68°C. At what temperature will the average kinetic energy of its molecules be twice that of –68°C?

• a) 137°C
• b) 127°C
• c) 100°C
• d) 05°C

Answer: 137°C

Question: An ideal gas is filled in a closed container and container is moving with uniform acceleration in horizontal direction. Neglect gravity. Pressure inside the container is

• a) Less in front
• b) Less at back
• c) Less at top
• d) Uniform everywhere

Answer: Less in front

Question: One kg of a diatomic gas is at pressure of 8 × 10⁴ N/m². The density of the gas is 4 kg/m³. The energy of the gas due to its thermal motion will be

• a) 5 × 10⁴ J
• b) 3 × 10⁴ J
• c) 4 × 10⁴ J
• d) 7 × 10⁴ J

Answer: 5 × 10⁴ J