Re: DBowman's Def 4

[John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU>]

On Thu, 15 Nov 2001, Jim Green wrote:

> 1) The only situation where this matters is the ubiquitous adiabatic
> cylinder and piston which is operated reversibly. I don't know of any other
> cases where "macroscopic" work doesn't change the entropy (ie is not both Q
> & W). I would be delighted to be shown others where this can be
> analytically demonstrated. This situation leads John Denker and me to worry
> about the value of the First Law.

I'd correct this to say that the "only" situation where it matters
is *any* situation in which work is done in a quasistatic
adiabatic (i.e., isentropic) manner.  (Damn the tautologies, full
speed ahead!)

For instance, take a thermally isolated paramagnetic substance and
change the magnetic field slowly.  Doing so alters the energy
levels of the spin states without altering their occupation
numbers and is, therefore, "pure" work.  This is the basis of the
adiabatic demagnetizaion refrigerator.  It is closely analogous to
the way that moving the piston slowly while thermally isolating
the gas alters the translational kinetic energy levels of the gas
without altering their occupation numbers.  Again, "pure" work.

John Mallinckrodt      mailto:ajm@csupomona.edu
Cal Poly Pomona          http://www.csupomona.edu/~ajm