From: phys-l-bounces@carnot.physics.buffalo.edu on behalf of John Denker
Sent: Mon 11/5/2007 4:57 PM
Ah, well, that illustrates my point that people have a
devil of a time figuring out what is "heat" and what is
"work", especially when dissipation is involved.
I don't want to get involved in a holy war about terminology,
but let us observe in passing that according to *some*
schools of thought, a resistor that can be immersed in water
would be called a "heater". If you to the store and ask for
an "immersion heater", that's what you get.
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Bob LaMontagne comment:
That is exactly why I used that example. If you include the heater within the boundary that you call a system, then it's traditionally called work - if it's considered to be outside the boundary, then it is heat. I find that to be untenable. I totally agree with dropping distinctions between dw and dq.
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That school of thought has some merit, i.e. some basis in real
objectively-observable physics. In particular, if we consider
the *state* of the water, as described by state variables E, T,
S et cetera, the change in state of the water (under the influence
of the immersion device) is well described by the T dS term in
the equation
dE = -P dV + T dS [1]
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Bob LaMontagne comment:
Actually, I like to use [1] as my mental picture for my personal definition of macroscopic entropy. Calculate the non-Pdv portion of dE, (i.e., dE+PdV), and divide by T. It brings home the idea that if the energy transfer is at low T the energy becomes less available (higher dS) than at high T (lower dS).
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Please excuse the Hake-like separators, I am using the email software from someone else's computer.