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# Physics VSQs for Class 11 with Answers Chapter 13 Kinetic Theory

Very Short Answer Type Questions [1 Mark Each]

Q.1. For ideal behavior of a gas, state the condition in terms of density of the gas.

Answer Answer: For ideal gas, P = ρRT
For ideal behavior, ρ should be low.

Q.2. The velocities of three molecules A,B,C of a gas are 3V, 4V, and 5V respectively. Calculate the R.M.S velocity?

Answer Answer:

Q.3. The ratio of vapour densities of two gases at the same temperature is 4 : 9. Calculate the ratio of their r.m.s velocities of molecules.

Answer Answer:

Q.4. A container filled with Helium gas at 300 K is heated to 600K. The coefficient of thermal expansion of the container is negligible. Calculate the change in the average K.E. of the helium atoms.

Answer Answer:

Q.5. The pressure of a gas at –173°C is 1 atmosphere, what should be the temperature of the gas when the pressure is 2 atmosphere if the volume of the gas is kept constant?

Answer Answer:

Q.6. The absolute temperature of a gas is increased 2 times. What will be the increase in r.m.s velocity of the gas molecules?

Answer Answer:

Q.7. Nitrogen and hydrogen gas are taken at the same temperature. What will be the ratio of the kinetic energies of nitrogen and hydrogen molecule when nitrogen is 14 times heavier than hydrogen?

Answer Answer: Both will have the same K.E. and ratio will be 1 : 1.

Q.8. 2 cm3 of oxygen and 2 cm3 of nitrogen gas are taken at N.T.P. Which will have larger number of molecules?

Answer Answer:Both will have the same number of molecules as Avogadro’s hypothesis says equal volumes of all gases contain equal number of molecules.

Q.9. There are N no. of molecules of a gas in a container. It is increased to 2N. Explain, with reason, how the pressure, total energy and r.m.s speed of the gas will change?

Answer Answer: It doesn’t depend on the no. of molecules. So, it remains unchanged.

Q.10. When a scooter runs for a long time, the air pressure in its tyres increases slightly.

Answer Answer:On running the scooter, the work done against friction is converted to heat.
P α T , so, as the temperature of the tyre increases, pressure will also increase.

Q.11. On what factors does the average kinetic energy of gas molecules depend : Nature of the gas, temperature, volume?

Answer Answer: The average kinetic energy of the molecules of a gas depends only on temperature i.e., Eav = f (T).

Q.12. Obtain the dimensional formula for R used in the ideal gas equation PV = RT.

Answer Answer:

Q.13. What is the relation between ratio of specific heats g and degree of freedom f of an ideal gas ?

Answer Answer:

Q.14. At what temperature does all molecular motion cease ?

Answer Answer: Absolute zero.

Q.15. Compare the mean kinetic energy of one mole of Helium and Nitrogen at the same temperature.

Answer Answer: Since mean kinetic energy per mole depends only on temperature, hence it will be same for Helium and Nitrogen.

Q.16. At 0K, which of the following properties of a gas will be zero. K.E., P.E., Vibrational energy, Density ?

Answer Answer: Since K.E. α T and vibrations are excited only at high temperature, hence K.E. of vibrational energy will be zero at 0K.

Q.17. If in an isothermal process, pressure is decreased then what will be its effect on mean free path ?

Answer Answer:
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