Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Definition of Capacitance

We, as physicists, often seem to be stuck with various conventions and
definitions. These conventions are often not the most convenient or most
logical, but once they get ingrained, they seem almost impossible to adjust.

Today's inconvenient convention is capacitance (and I bet I could come up
with one a day for the next month). There are two obvious ratios we could
C = Q/V
C' = V/Q

The first, of course, is the standard definition of capacitance, but the
second is much more logical because it then matches R & L:

1) similar definitions:
C' = V / Q
R = V / (dQ/dt)
L = V / (d2Q/dt2)

2) Similar geometry (at least for "standard" geometries):
C' = (1/e0) l/A (l = length; 1 = one)
R = (rho) l/A
L = (mu0 N^2) l/A

3) Similar addition rules:
For all three - in series, you simply add values
- in parallel, you add inverses.

I can't think of a single case where this definition is inferior (except, of
course, for historical inertia). Think of all the time and confusion we
could save our students. Now we just need to hire a good ad agency and/or
grease the palms of a few textbook editors ;-)

Tim Folkerts