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*From*: John Clement <clement@HAL-PC.ORG>*Date*: Fri, 13 Feb 2004 17:07:48 -0600

I would vote for the converse solution. Go with conductance and then define

an inverse inductance (outductance?, niductance?...)

The then means that the quantities are related in a simple way analogous to

position, velocity, acceleration.

The quantity capacitance has a very easily pictured meaning as the amount of

charge for a given voltage.

Similarly the conductance is also easily pictured as the amount of flow of

charge (current) for a given voltage. This also makes it correspond to

experiments where students vary the voltage and measure the current. It

might make teaching much easier. Resistance is probably conceptually a much

harder concept.

Of course if we are really willing to reform things then we need to consider

Ben Franklin's mistake that saddled us with + and - because he did not know

which way the charge was usually transferred. Then we could help students

conceptually because the current would be in the same direction as the

electron flow.

Whether or not such a rationalization of the system would help students can

only be ultimately decided by experiment. Does anyone know of any good

experiments that relate to this issue.

John M. Clement

Houston, TX

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

consider:

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

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