4. (a) State the assumptions made in the derivation of the Bose-Einstein distribution 1 function for photons, f(e) == kBT -1 (3 marks) Derive the density of states, g(e), for a two-dimensional box of photons confined in (3 marks) (b) area, A. (c) Hence determine the temperature dependency of the total energy of a two dimensional gas of photons. (4 marks)