## PHYS 317 - Reading Assignment #18

**Why is the average energy per atom related to the total thermal
energy U?**
A single atom can be thought of as the ``system'' and all the remaining
atoms thought of as the ``reservoir.'' We compute the average energy
for this single atom at this temperature. Then, since there was nothing
special about the atom we chose, we can conclude that all N atoms will have
the same average energy, so U = N*E_{avg}.

**What is the partition function for a single dipole (a "spin")
in the two-state paramagnet?**
Z = e^{beta*mu*B} + e^{-beta*mu*B} = 2 cosh(beta*mu*B).

**Where does the factor (2j+1) in equation (6.30) come from?**
For an angular mometum vector with magnitude j there are 2j+1 different
possible orientations, all different states but having the same energy.

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