The average electron energy in an electron gas is known to be <e>=3E(f)/5. The energy for N such electrons would be 3NE(f)/5. Find the pressure in terms of U and V, where V is the volume of the electron gas. My solution. Fermi energy E(f)=(h^2/2m)*((3N/8*pie*V)^(2/3)) therefore E(F) is proportional to V^(-2/3) since it is proportional i just have to plug into 3NE(f)/5 or the other one correct? Thanks. so which formula do i plug V^(-2/3) into E(F)? The 3NE(f)/5 or 3E(f)/5.