Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: W+Q deprecated



Responding to John, Jim, and Bob:

> Can you give me an example or two of a reversible process for which
this division into W and Q fails?

For starters, it fails for anything that isn't
at (or very near) thermal equilibrium.

But aren't reversible processes necessarily near equilibrium?

It also fails in a grand-canonical situation;
you would need additional terms on the RHS of
the "E=W+Q" expression.

Agreed. I should have explicitly stated that the number of particles
in the system is fixed.

I do not define S in terms of "Q" or T.
I consider entropy to be primary and fundamental.
Entropy is well-defined even in cases where the
temperature is zero, unknown, irrelevant, or
undefinable.

Yes, I agree that there are some interesting possibilities here. But
not in traditional classical thermodynamics I would think. Aren't you
diverging into information theory and other sidebars?

Let me chime in here: Can _you_ give an example or two where the First Law
as stated _is_ helpfully applied? -- ie a process where Q and W are both
present _and_ are both identifiable? _Except_ of course the ubiquitous
adiabatic cylinder and piston

Okay. I've got a gas of magnetic atoms. I slowly change the current
which flows both through a set of Helmholtz coils around the gas and
an electrical heater immersed in the gas.

Of course there's more, but let's pause for any comments.

Bob's starter looks fine to me, as far as my understanding extends.
--
Carl E. Mungan, Asst. Prof. of Physics 410-293-6680 (O) -3729 (F)
U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5026
mungan@usna.edu http://physics.usna.edu/physics/faculty/mungan/