Re: Thermo/Sidebar

[Jim Green <JMGreen@SISNA.COM>]

> >A calculation of deltaW seems straight forward but how would one calculate
> >deltaS?
>
> Uhhh, how about delta_Q over T?

Umm, alas no good -- I don't see here any agreement of just what deltaQ
might be except for the cylinder and hot plate case.

> >Can one calculate a density of states?
>
> A) Yes.
>
> B) Your original challenge (Thu, 25 Nov 1999 11:47:32 -0700) concerned
> *classical* thermodynamics.  I thought the whole point of classical
> thermodynamics (if there is a point, which is questionable) was to see how
> much one could do without saying anything about the microscopics.

I admit that, in my attempt to be as general as possible (as is my want in
asking questions), I do include stat mech in classical physics and I even
extend this to thermo  although my dear friend Sadi would not be all that
happy.  And, given that  the usual thermo presentation is based solely on
the cylinder and hot plate, I wonder about the point as well, but here we
are nevertheless...

> >5) Perhaps simplest of all, what about the thermodynamics of an adiabatic
> > >demagnetization refrigerator?
> >
> >In what sense are they macroscopic the way the classical cylinder is?
>
> In one part of the cycle, the demag stage absorbs heat

Enormous red flag!!!

> at constant
> temperature.  In another part of the cycle, it changes temperature at
> constant entropy.  It's just the same as the gas-cylinder story, except
> that the external variable is magnetic field, not cylinder-volume.

Yes, I am familiar with this process -- but not the name as you use
it.  But this may be a bit Byzantine for the masses -- and I don't see it
as microscopic/mechanical as I would like.  Let me think on it.

And tell me how to calculate deltaS in the deltaW phase from stats.

TX again.

Jim

Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen