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Re: Electrostatics problem



At 15:51 2/24/99 -0700, you wrote:
I just spent a short time wrestling with this question with one of my more
intuitive AP Physics student. I am stuck.

Given two conducting metal parallel plates, as an air capacitor. If we
place equal
charges of opposite sign on each plate, we would expect to find the charge
on the inner facing surfaces. If the signs are alike, the charges would
migrate to the outer surfaces. So far so good?

Is there a clear way ( I cannot think of it) to determine the charge
distribution if the two plates are charged unequally. We tried looking at
potentials and thinking that the final potentials will tend to a minimum
but found it hard to write any meaningful expressions for that.


Any help would be appreciated.

Ken Fox

This is off the cuff.
If I imagine a big capacitor connected to a battery, I can ascribe the
momentary current to a charge addition on one plate and a charge removal
of equal magnitude from the other plate.

On the other hand, if I add a charge to some isolated conductor, I
expect its potential to jump with respect to ground.
So I divide the unequal plate charges into equal and complementary
charges, and an extra charge which lifts the potential of the ensemble.

This model necessitates that I draw an image of three capacitors:
One, the capacitor under discussion
Two and Three: stray capacitance to ground from each electrode which
is the basis for the elevated voltage.

Using "Complete" capacitor models like this may ease the concept,
don't you think?

Brian

brian whatcott <inet@intellisys.net>
Altus OK