Re: Confused by a derivation.

[Bob Sciamanda <trebor@VELOCITY.NET>]

Each sheet contributes sigma/2epsilon.  The total field, due to the
universe (the two sheets in this case), is sigma/epsilon.
Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor
----- Original Message -----
From: "Ludwik Kowalski" <kowalskiL@MAIL.MONTCLAIR.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Sunday, February 03, 2002 3:56 PM
Subject: Re: Confused by a derivation.


> The field inside the conducting plate is zero. For that reason
> my expectation would be:
>
>           MMMMMMMMMMMMMMMMMMMMMM__________
>           MMMMMMMMMMMMMMMMMMMMMM
>           UPPER METALLIC PLATE  (no field inside)
>           ++++++++++++++++++++
>            | | | | | | | | |                contributes +sigma/eps-o
>            v v v v v v v v v
>
>
>            | | | | | | | | |                contributes -sigma/eps_o
>            v v v v v v v v v
>           - - - - - - - - - - - - - - - - - - - -
>           LOWER METALLIC PLATE (no field inside)
>           MMMMMMMMMMMMMMMMMMMMMM__________
>           MMMMMMMMMMMMMMMMMMMMMM
>
> What is wrong with this reasoning?
> Ludwik Kowalski
>
> John Mallinckrodt wrote:
>
> > On Sun, 3 Feb 2002, Ludwik Kowalski wrote:
> >
> > > ... two layers of sigma in a capacitor reside on metallic
> > > plates and each plate produces E"=sigma/eps_o.
> >
> > No.  Gauss' law shows that each layer produces sigma/(2*eps_o) on
> > each side of the layer.  The result from the + layer looks like
> > this:
> >
> >           ^ ^ ^ ^ ^ ^ ^ ^ ^
> >           | | | | | | | | |
> >           ++++++++++++++++++
> >            | | | | | | | | |
> >            v v v v v v v v v
> >
> > When the effect of the - layer is included we find that the field
> > between the plates is sigma/eps_o and elsewhere it is 0.
> >
> > John Mallinckrodt      mailto:ajm@csupomona.edu
> > Cal Poly Pomona          http://www.csupomona.edu/~ajm