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Re: Meauring Volts?



On Mon, 09 Dec 2002 17:17:16 -0500 Ludwik Kowalski
<kowalskil@MAIL.MONTCLAIR.EDU> writes:
On Monday, December 9, 2002, at 12:30 PM, Jim Green wrote:

Ludwik, should we stop discussing the "flowability" of "energy"
and "heat"? Is that discussion also meaningless?

No. To illustrate what is usually meant by this let me invent
a trivial problem. You have two identical tanks with 10 kg
of water. The tanks are coated with thick layers of Styrofoam.
The constant temperature in the tank A is 90 C and that in
B is 20 C. The heat capacity of containers is negligible in
comparison with that of water.

At time zero a thick silver rod is used to link the containers.

*** How much of the rod length, if any, is exposed to the air?
*** Is the silver rod parallel to the surface of the water in the tanks?
*** Is the silver rod closer to the top, middle or bottom of each tank?
( Remember that the density of water depends on its temperature)

The temperature of A starts going down while that of B starts
going up. The rod is removed when the temperature of A
becomes 65 C and temperature of B becomes 43 C.

*** Is thi a special kind of water that heats or cools instantaneously
throughout its entire volume?? If not, further details are needed
for
the gremlin to know exactly when to remove the rod?

1) How much thermal energy (heat) was lost by A?
Q1=c*m*dT1=1*10000*25=250,000 cal

*** OK so far,... assuming that the water was free of dissolved
impurities.
2) How much thermal energy (heat) was gained by B?
Q1=c*m*dT2=1*10000*23=230,000 cal

*** No! It is not logical to use the same term (Q1) for equation 1
and also in equation 2 unless you are postulating
in advance that these two terms are identical.

3) What happened to the missing 20, 000 calories
of heat? Part of it was probably still in the rod and
the rest in the surrounding air.

**** Possibly Yes, and possibly No!. You forgot to state the
initial and the final temperatures of the air and of the rod.

4) Is it correct to say that 230,000 calories of heat
(thermal energy) was transferred (flowed) from
A to B? WHY NOT?

*** Yes! It is perfectly correct to say that 230,000 calories
of heat were successfully transferred (assuming reasonable
responses to my questions above). It is also reasonably
correct to say that an additional 20,000 calories of heat
were lost to the two-tank system during the transfer
process.

If my memory is reliable, problems of that nature were
modeled it terms of caloric, a fictitious substance. The
concept of thermal energy, and of molecular motions,
were introduced much later. What was wrong with this?

*** It would appear that the responses to all of your questions,
above would not differ much if you base your reasoning in
accordance with the caloric theory or with the kinetic-molecular
theory. Apparently, I either either misread some of your arguments or I
failed to interpret them correctly. Would you please set me straight!
Thanks.

Herb Gottlieb from New York State
(Where we believe that heat can be lost during a transfer process,
making the transfer of the heat less than 100% efficient .....
BUT WHAT HAS THAT TO DO WITH THE TITLE OF THIS
DISCUSSION, "MEASURING VOLTS???)