Deriving heat capacity using thermodynamics identity

[ultimateguy]

Homework Statement

Use the thermodynamic identity to derive the heat capacity formula C_V=T\frac{\partial{S}}{\partial{T}}_V

Homework Equations

C_V=\frac{\partial{U}}{\partial{T}}
T=\frac{\partial{U}}{\partial{S}}
dU=TdS-PdV+\mudN

The Attempt at a Solution

I used C_V=\frac{\partial{U}}{\partial{S}}\frac{\partial{S}}{\partial{T}}=T\frac{\partial{S}}{\partial{T}}_V=\frac{\partial{U}}{\partial{T}}=C_V.
This is the only solution I can think of, but I don't think I used the thermodynamics identity, did I?

 

[Kurdt]

There are a distinct lack of thermal physicists on this website and with good reason as it is one of the most boring subjects ever. I think if you know that:

dS=(\frac{\partial{S}}{\partial{U}})_{PV}dU

Then you can substitute the following into the equation for dU,

dU=(\frac{\partial{U}}{\partial{T}})_VdT

and have a fiddle about, that should set you off on the right lines.

 

[ultimateguy]

This may be a dumb question, but what's the difference between E and U?

 

[Kurdt]

This may be a dumb question, but what's the difference between E and U?

There is none. I apologise. I normally write E and I was trying to conform to your notation but obviously forgot half way through I will change it.

 

[dextercioby]

The solution provided by the OP is correct.

Daniel.

 

[Kurdt]

I'd have thought if they wanted a derivation from the thermodynamic identity then they'd want you to start from that. However the OP proof might be accepted.