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Re: AC electricity



At 02:19 PM 1/17/01 -0700, Larry Woolf wrote:
I personally like the analogy of the pin ball machine. The pins represent
the fixed ions in the lattice. The balls represent the free electrons.
When the machine is tipped one way (positive voltage across the resistor),
the balls (electrons) flow downhill and bump into the pins (dissipating
energy - heat).

One must be careful with such analogies. In a pinball machine, there can
be local accumulations of balls here and there. In the regime where
Kirchhoff's laws apply, this does not happen with electricity.

Yes, no analogy is perfect, but the gist of the physics is in this analogy
- dissipation of energy by collision, the effect of the applied voltage,
the constant acceleration between scattering events, and much slower drift
velocity. For a nice discussion take a look at chapter 4 in the berkeley
physics course electricity and magnetism book (volume 2 of this series) by
Edward Purcell -I have the 1965 edition.

Dr. Lawrence D. Woolf; Phone: (858)-455-4475; www.sci-ed-ga.org
General Atomics; 3550 General Atomics Court; San Diego CA 92121-1194