(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

An evacuated container with volume V and at a temperature T contains black body radiation with an energy density equal to 4[tex]\sigma[/tex]T^{4}/c

I Determine the heat capacity at constant volume of the radiation

II Hence show that the entropy of the radiation is given by

S(T,V)=16[tex]\sigma[/tex]VT^{3}/3c (can't seem to get the sigma to display correctly here)

III The container is placed in thermal contact with a heat bath at temperature Tr. If the heat capacity of the cavity material itself is negligible, show that the overall change in entropy of the universe after the system and heat bath have reached thermal equilibrium is

[tex]\Delta[/tex]Stot=(4[tex]\sigma[/tex]VT_{r}^{3}/3c)(1-t^{3}(4-3t))

t= T/T_{r}

IV comment on the sign of [tex]\Delta[/tex]Stot as a function of t

2. Relevant equations

3. The attempt at a solution

Have done I and II correctly. IV looks fine.

Just need a little nudge as to how I should start III, I just can't think of the appropriate formulae at the moment. So any links to references etc are greatly appreciated.

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# Homework Help: Black body radiation entropy question

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