PHGN341 - Thermal Physics
Spring 2013
Homework 5
Due Friday, February 15
1. DVS: 3.5 (p. 91) (Recall that problem 2.17 was worked in class and can be obtained
from Eq. 2.21 by invoking the q <---> N symmetry of the multiplicity.)
2. DVS: 3.8 (p. 93)
3. DVS: 3.10 (p. 97)
4. DVS: 3.14 (p. 97)
5. Applying the virial theorem to a gravitationally bound star, one has:
2 <KE> = - <PE>. Thus, the total energy is U = <PE> + <KE> = - <KE>. Using the
equipartition theorem, one has <KE> = 3 N k T/2. For a fully ionized star consisting
only of hydrogen, N = 2 M*/mp, where M* is the mass of the star and mp is the mass
of a proton (the factor of two arises because each hydrogen atom when fully ionized
contributes one proton and one electron.)
a. Estimate the temperature of a hydrogen star of one solar mass.
b. What is the change in the temperature of a star when heat Q is added as from
nuclear reactions? Explain.
c. What is the change in the entropy of the star when heat Q is added?