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Re: [Phys-l] T dS versus dQ

To be more specific:

I wanted an easily constructed device wherein one may demonstrate the difference between entropic and isentropic addition of energy into a gas. True, doing both mechanically would be better, but as I wrote, I think it's expensive to do that. I just "now" thought, why not add energy very slowly via the heater and compare w/ rapidly, BUT that would make a very great demand on the insulation. I suppose (from the advanced lab list) one could jacket the cylinder w/ a PID controlled heater to match the temp inside**.

BTW anybody know the functional relationship of rate of compression w/ the rate of increase of S?

** like a guard element in an electrical experiment or an accelerating cage in a direct measure of g.


On 2010, Jan 18, , at 17:08, chuck britton wrote:

At 4:47 PM -0800 1/18/10, Bernard Cleyet wrote:
I shoulda used "skeptical". and added I hope they will be.

RE: creating entropy. I'm further confused. I thought adding E via
a heater would be entropic while adding E via P dV (slowly*) would
be isentropic, with the end states being different for the same E.

If I'm getting this right - the heater WOULD be just as 'entropic' as
the speaker is. The speaker is a closer analog of fast moving piston.
The 'mechanics' of the heater are way different. Speaker is still
'mechanical'. I think that it is the similarity of the speaker to the
piston that is being stressed.
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