# System with entropy k ln 2

1. Jul 22, 2015

### Philip Wood

An old book I have on elementary Statistical Mechanics (Rushbrooke) uses as an especially simple case a system with one energy level. This level is doubly degenerate. The author doesn't give an example of such a system. Can anyone think of one? And would it have entropy $k\ ln 2$?

[My thoughts turn to spin 1/2 particles but I'd like comment.]

2. Jul 22, 2015

### Dr. Courtney

Real systems tend to have more than two energy levels, but some are approximated as two level systems in certain situations.

3. Jul 22, 2015

### TeethWhitener

Yes, a spin 1/2 particle has a doubly degenerate energy level in the absence of a magnetic field.

4. Jul 22, 2015

### Philip Wood

DrC and TW. Many thanks for replying.

TW: would you, then, say that a spin 1/2 particle, viewed as a system, has an entropy of $k\ ln2$ in the absence of a magnetic field?

5. Jul 22, 2015

Yes.