Bob Carlson wrote
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In a message dated 98-02-19 22:34:21 EST, Bob Sciamanda writes:
<< An instructive parallel is marbles falling through syrup in the earth's
gravitational field. They travel at a terminal velocity, serving in
effect as a mechanism for transforming into heat the work done by the
earth's gravitational field. In the electrical current carrying wire
electrons are falling through an electrostatic field (due to surface, etc
charges) at a terminal velocity (effectively) and "immediately" giving
that energy up to the lattice as heat.
>>
I didn't imagine this as being such a smooth, continuous process. Before the
E field is present, I imagine a randomized nature for the motion of the
electrons in the resistor. Hence, if we looked at a cross section, then we
would see (on the average) as many electrons crossing left as right across
this cross section. When the E field is present, I imagine this to cause a
net flow of electrons across the cross section. However, I do not imagine
that all electrons will be traveling so harmoniously together inside the
resistor, with the same constant velocity, just because the E field is
present.
Bob Carlson
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Of course, you're right. My model simply chooses one possible
microscopic state (among zillions) which give the observed
macroscopic results - it's a convenient calculational and conceptual
model. (Who knows what the "true" model "looks like?).
At the introductory level, I also "derive" the ideal gas equation by
specifying N/3 point molecules travelling with the RMS velocity in
each of the three Cartesian directions. (A commonly exploited
simplification - and illumination).