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At 01:30 PM 3/5/01 -0500, Bob Sciamanda wrote:voltmeters
The trivial case of a single conductor: Q = C V is useful. C is a
constant of geometry, even for various values of Q and V. IOW one need
not involve the the "sphere of charge at infinity" - the equations are
still valid and useful.
When I see the scalar equation
Q = C V
I assume it is shorthand for
Q = C delta V
= C (V1 - V2)
where V1 and V2 are the voltages on the two terminals of the
capacitor. That is a fine equation, valid and useful. The expression
(V1-V2) is manifestly gauge invariant.
If somebody wants to interpret
Q = C V
in terms of some "absolute" voltage V, then the equation does not look
valid to me. It begs the question of how to measure V. All the
I've ever seen have *two* leads, and can only measure a voltage*difference*.
. . .