[UPSC IFoS 2019] Statistical Physics (Q269, 5+10=15M)

Consider a quantum -- mechanical gas of non-interacting spin zero bosons, each of mass m which are free to move within volume V. (i) Find the energy and heat capacity in the very low temperature region. Discuss why it is appropriate at low temperatures to put chemical potential equal to zero. (ii) Show how the calculation is modified for a photon (mass = 0) gas. Prove that the energy is proportional to \text{T}^4.