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Re: Confused by a derivation.



Addendum: More hopefully, try it with concentric right circular
cylinders - the transition to planes is then easier and more intuitive.

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor
----- Original Message -----
From: "Bob Sciamanda" <trebor@VELOCITY.NET>
To: <PHYS-L@lists.nau.edu>
Sent: Tuesday, February 05, 2002 1:21 PM
Subject: Re: Confused by a derivation.


Michael,
If you want to get this result (no charge on outside surface) directly
from Gauss' law then I would try changing to (or beginning with) a
capacitor of two concentric spheres - equally and oppositely charged.
Here I think you can use Gauss' law and symmetry to argue to zero field
on
the inside surface of the smaller sphere. (?) The parallel plate
geometry
doesn't give you this nicety, but you might wave your hands and deform
the
apheres into planes and draw conclusions. :)

I'm only guessing, I don't advise this method. I would not expect
Gauss' law to directly do everything - it can't. It can rigorously give
you the field of each charge sheet - then the superposition principle
can
rigorously give your desired result.


Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor