# Density of states of ideal gas and photon gas

## Homework Statement

I know how to derive the density of states for an ideal gas by using the energy equation:

E_n = A*n^2, where A = (h_bar^2*pi^2)/(2mL^2)

but what about for a 'photon gas'? Do I use the same energy equation as above, or the following:

E_n = (h_bar*pi*c/L)*n

## The Attempt at a Solution

I think I'd use the second equation, but solutions to the assignment said use the first equation. I'm confused!