## PHYS 317 - Reading Assignment #17

1. What does it mean for an energy level to be degenerate?

When two or more different microstates have the same energy level, then we call this energy level degenerate (basically, knowing the energy isn't enough to specify a unique microstate).

2. What must we assume about the entropy change of the reservoir to go from equation (6.2) to (6.5)?

We need to assume that the PdV contribution is negligible compared to the dU contribution.

3. What is the name (in words) for the sum of Boltzmann factors over all possible states?

The partition function. Don't ask me why.

4. How many hydrogen atoms out of a billion are in the first excited state at a temperature of 5800 K?

The "first" excited state is really 4 different states [for those up on quantum mechanics, we have (n,l,m) values of (1,0,0), (1,1,1), (1,1,0), and (1,1,-1).] For each of those states we have a probability around e^(-20). Multiplying by 4 gives 5.6 atoms out of a billion in the first excited state.