From: "Christopher R. Carlen"
Subject: Re: What's E-field in a capacitor?
Date: Wed, 06 Nov 2002 18:14:11 -0800
Organization: Sandia National Laboratories, Albuquerque, NM USA
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NNTP-Posting-Date: Thu, 7 Nov 2002 01:13:08 +0000 (UTC)
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Roy McCammon wrote:
> "Christopher R. Carlen" wrote:
> Some comments
> 1. If you take a single plate and plop some charge on it,
> the charge does not distribute itself uniformly; it crowds
> toward the edges; it tries to get away from the other like
> charges. E_vec = n_hat Q/(A p) does not apply because Q
> is not uniform.
> 2. Take two such plates and charge them oppositely and
> then put them parallel with a small separation, each
> bit of charge is still trying to get away from like charge,
> but it is trying to get closer to the opposite charge
> on the other plate. In a sense, the whole thing is neutral,
> so the the charge is more uniformly distributed.
> 3. If you work with a capacitor made from two concentric
> hollow spheres, the charge has to distribute it self
> uniformly. Now take Q off the inner sphere and put it
> on the outer sphere. Because of symmetry, there is
> no field at all inside the inner sphere. In the space
> between the two spheres the field is entirely due
> to the charge on the inner sphere. Outside the outer
> sphere, the fields from both sphere superimpose to
> give zero.
Interesting additions to the discussion. Thanks.
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA