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# Re: Definition of Capacitance

Tim writes:

... I can't think of a single case where this definition is inferior
(except, of course, for historical inertia) ...

Although I agree with most of your posting, a couple of thoughts:

1) You left off another point in your favor--the increased esthetic
beauty of the mechanical analogy with masses, viscous drag
coefficients, and springs.

2) There is at least one case, however, in which the proposed
definition of capacitance is at least a little bit, and maybe quite
inferior--that which arises when one wants to think (as one does more
often than not) about how much charge or energy a "capacitor" will
store for a given voltage. It just makes more sense in such
situations that the bigger the "named characteristic of the device"
the bigger the resulting charge or energy. We already have this
"problem" with springs: The bigger the spring constant, the less
energy the spring will store for a given applied force.

3) One *can*, of course, accommodate your concern by changing the
definitions of the *other* quantities: "Resistance" becomes
"conductance" (in mhos, and "conductors" in parallel add) and
"inductance" becomes ... well I don't know what "inductance" becomes,
maybe it just stays "inductance." After all we speak of "induced"
currents just as much as we do "induced" voltages. In the process,
of course, we replace the direct mechanical correspondences with
inverse correspondences. Moreover, although I have some warm fuzzies
for "conductance," I am less happy about inverse inductance.

--
John Mallinckrodt mailto:ajm@csupomona.edu
Cal Poly Pomona http://www.csupomona.edu/~ajm