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Re: [Phys-l] T dS versus dQ

That is a different process than we were discussing. When done slowly the process is basically isothermal because of the heat going through the walls. When done quickly, the process is close to adiabatic because there is little time for energy transfer through the walls.

We use that apparatus in lab for some of our general physics sections. The screw is hard to turn and we have never been able to turn it fast enough to see a temperature change. For all intents, we give it to our students as a way of graphing P versus V when T is constant.

Can you share how you manage to turn the screw that fast? I would love to add temperture to the lab as well.

Maybe ours are just stiffer than yours to turn.

Bob at PC
From: [] On Behalf Of WC Maddox [maddox@physics.Auburn.EDU]
Sent: Thursday, January 14, 2010 4:28 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] T dS versus dQ

From: WC Maddox

The experimentalists among those receiving these Tds vs dQ messages may
want to show the temperature difference between slow pressure increase
and rapid pressure increase by using the device shown here: It has a digital
temperature display. If you turn the screw slowly you will not see a
temperature change. If you turn the screw rapidly you get ~ 1 degree (C)
increase for full travel of the piston. This is with the only insulation
being the plastic tube. You can then demonstrate cooling during
expansion by turning the screw the other way rapidly.

End Message
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