NCERT Class 11 Physics Chapter 13 Kinetic Theory CBSE Board Sample Problems

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Question 20:

The container shown in Fig. 13.6 has two chambers, separated by a partition, of volumes litre and litre. The chambers contain moles of a gas at pressures . Calculate the pressure after the partition is removed and the mixture attains equilibrium.

Answer:

For 1 mole

For moles

Total energy is

Comment: This form of ideal gas law represented by Equation marked* becomes very useful for adiabatic changes.

Question 21:

A gas mixture consists of molecules of types A, B and C with masses . Rank the three types of molecules in decreasing order of (a) average speeds.

Answer:

The average K.E will be the same as conditions of temperature and pressure are the same

Question 22:

We have of hydrogen gas in a cubic chamber of size kept at NTP. The gas in the chamber is compressed keeping the temperature constant till a final pressure of atm. Is one justified in assuming the ideal gas law, in the final state?

(Hydrogen molecules can be consider as spheres of radius).

Answer:

We have molecules, each of volume .

Molecular volume

Supposing Ideal gas law is valid.

Final volume

which is about the molecular volume. Hence, intermolecular forces cannot be neglected. Therefore the ideal gas situation does not hold.

Question 23:

When air is pumped into a cycle tyre the volume and pressure of the air in the tyre both are increased. What about Boyle’s law in this case?

Answer:

When air is pumped, more molecules are pumped in. Boyle’s law is stated for situation where number of molecules remain constant.

Question 24:

A balloon has mole of helium at . Calculate

(a) The number of atoms of helium in the balloon,

(b) The total internal energy of the system.

Answer:

No of atoms

Average kinetic energy per molecule

Total internal energy

Question 25:

Calculate the number of degrees of freedom of molecules of hydrogen in 1 cc of hydrogen gas at NTP.

Answer:

Volume occupied by 1gram mole of gas at

Number of molecules in 1cc of hydrogen

As each diatomic molecule has degrees of freedom, hydrogen being diatomic also has degrees of freedom

Total no of degrees of freedom

Question 26:

An insulated container containing monoatomic gas of molar mass m is moving with a velocity . If the container is suddenly stopped, find the change in temperature.

Answer:

Loss in K.E of the gas

Where

If its temperature changes by then