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[Phys-L] irreversible quasistatic



I'm often uncertain about the idea of irreversible quasistatic processes,
mostly because thermo textbooks don't give many examples.

Would the following process be an example of such a process? Explain why
not if you don't think so.

One hot plate at temperature T_H is parallel to a cold plate at T_C. The
plates are oriented vertically with a small pendulum ball suspended between
them. The ball is set swinging, so that it hits the plates at the end of
its motion back and forth. The ball carries small increments of thermal
energy dE from the hot plate to the cold plate. The time t when the ball is
swinging through free space between the two plates allows the two plates to
re-equilibrate internally. In this way each plate is ever only
infinitesimally out of thermal equilibrium, yet I am accomplishing a net
energy transfer from the hot to the cold plate.

You can arrange to make the ball as small as you like and the plates as far
apart as you like to ensure you make dE as small as you like and t as long
as you like, to keep as close to equilibrium for each plate as you like.

As you can see, I have drawn inspiration for this idea from the familiar
"Franklin's bells" setup for charge transfer between capacitor plates, as
well as the notion of how one can accomplish an irreversible quasistatic
expansion of an ideal gas in a piston with kinetic friction by making the
piston expand only in infinitesimal steps dx at a time.

--
Carl E. Mungan, Professor of Physics 410-293-6680 (O) -3729 (F)
Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-1363
mailto:mungan@usna.edu http://usna.edu/Users/physics/mungan/