## PHYS 317 - Reading Assignment #23

**In equation (7.42), why is the total energy less than N*epsilon**_{F}?
N is the number of particles in the system. As they fill up the available states from lowest energy upwards, they take energies from 0 to epsilon_{F}. Therefore the average energy per particle must be less than epsilon_{F}.

**In going from a T=0 fermion gas to a T>0 fermion gas, is it accurate to say that each fermion gains an energy of roughly kT? **
Absolutely not. Only a fermions within an energy of kT of the Fermi energy can possibly go to an excited with a thermal energy of kT. This is a often tiny fraction of the actual fermions.

**What is the physical origin of degeneracy pressure? **
Basically the Pauli exclusion principle. It forces an ideal electron gas to contain highly energetic electrons, and these provide a significant pressure even at absolute zero.

**Give a definition for the density of states g(epsilon) in words. Hint: look around equation (7.50), not later. **
The number of single-particle states per unit energy. So integrating over energy give the number of single-particle states.

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