Deriving Average Energy of an Oscillator: Thermal Radiation

[sai2020]

The question:

In 1900, Planck used an abstract model consisting of harmonic oscillators with various frequency. Derive an average energy \bar{\epsilon} of a single oscillator where the oscillators of frequency f can only take on discrete energies \epsilon_{n} = nhf, n=0, 1, 2, ... and the Boltzmann probability distribution, P(\epsilon_{n}) = exp(-\epsilon_{n} / k_{B}T). (Note: Boltzmann showed that the probability for a system at equilibrium to have an energy E is proportional to exp(-\epsilon_{n} / k_{B} T, where k_{B} is the Boltzmann constant.

I have no idea what he is talking about and my textbook doesn't say anything either. Can someone point me to a good book about these stuff?

 

[mangoo87]

R. Eisberg, R. Resnick
Quantum physics of atoms, molecules, solids, nuclei and participles

 

[sai2020]

Thanks a lot. It's a beautiful book