1. The problem statement, all variables and given/known data

A cavity contains black body radiation at temperature T = 500 K. Consider an optical mode in the cavity with frequency ω=2.5×10$^{13}$ Hz. Calculate

a) the probability of finding 0 photons in the mode
b) the probability of finding 1 photon in the mode
c) the mean number of photons in the mode.

2. Relevant equations

Possibly <n> = $\frac{1}{exp(\frac{\hbar \omega}{k_{b} T})}$

3. The attempt at a solution

Plugging the numbers into the equation above gives the answer to c (I think), which comes out to 1.855. However I thought that you could only have 0 or 1 photons in a given mode.

Not sure how to go about a) and b).

http://ift.tt/1jYEXuC