21.
If the partition function of a harmonic oscillator with frequency $$\omega $$ at a temperature T is $$\frac{{kT}}{{\hbar \omega }},$$  then the free energy of N such independent oscillators is

22.
The free energy for a photon gas is given by $$F = - \left( {\frac{a}{3}} \right)V{T^{ - 4}},$$    where a is a constant. The entropy S and the pressure p of the photon gas are

24.
Which one of the following statements is not true?

26.
Consider black body radiation in a cavity maintained at 2000 K. If the volume of the cavity is reversibly and adiabatically increased from 10 cm3 to 640 cm3, the temperature of the cavity changes to

27.
For a two-dimensional free electron gas, the electronic density n, and the Fermi energy EF, are related by

28.
Consider a system of N atoms of an ideal gas of type A at temperature T and volume V. It is kept in diffusive contact with another system of N atoms of another ideal gas of type B at the same temperature T and volume V. Once the combined system reaches equilibrium,

29.
The internal energy of n moles of a gas is given $$E = \frac{3}{2}nRT - \frac{a}{V},$$    where V is the volume of the gas at temperature T and a is a positive constant. One mole of the gas in state (T1, V1) is allowed to expand adiabatically into vacuum to a final state (T2, V2). The temperature T2 is

30.
Consider a system of two non-interacting classical particles which can occupy any of the three energy levels with energy values E = 0, ε and 2ε having degeneracies g(E) = 1, 2 and 4 respectively, The mean energy of the system is