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Re: How many volts ?



On Tue, 25 Mar 1997, LUDWIK KOWALSKI wrote:

Bob Sciamands wrote:

You're going to have a tough time getting the field inside these plates
to be zero!

He was responding to

.... Thus an isolated circular plate of very large radius will create
the field which is the same as that due to a uniform circular loop
(a thin wire).

Yes, this is not than what I wanted to say. Let me correct it now.

Thus an isolated circular plate of very large radius will create
a charge density (on both sides) which increases with the radius.
Why should this interfere with E=0 inside a circular plate?

As you can see, Bob, I am waving hands hoping that somebody will prove, or
disprove, my intuitive argument about a single isolated plate. I suspect
that the minimum potential energy will correspond to an axially symmetric,
but not uniform, distribution of initial charge on a single plate. But I
do not know what to think about the final distribution of charges (when
plates are very close to each other). Why should we take it for granted
that the minimum energy requirment, when |Q1| and |Q2| are not equal, is
the same as for equal charges (for two uniform distributions)? I would
like this to be demonstrated (experimentally, analytically or numerically).

Ludwik Kowalski kowalskiL@alpha.montclair.edu

I'm as confused as a Physics major taking the graduate record exam. I
think that John has the solution right for the difference in potential
for two plates which may be considered infinite. That is, those charges
were charge densities!

There are two things here that this solution doesn't tell us much about:

1. What happens if the plates are not infinite. I think
this is at least part of Ludwik's objection.

2. What happens to the potential difference between the
plates as they are moved together. After all, they
were infinitely far apart originally. I presume that
the total potential would go down since they attract
each other.
other and work will be done by the field.


W. Barlow Newbolt 540-463-8881 (telephone)
108 Parmly Hall 540-463-8884 (fax)
Washington and Lee University newbolt.w@fs.science.wlu.edu
Lexington, Virginia 24450 wnewbolt@liberty.uc.wlu.edu

"The best measure of a man's honesty isn't his income tax return. It's the
zero adjust on his bathroom scale"
Arthur C. Clarke