Re: IONS/metal pedagogy

["Bob Sciamanda" <trebor@velocity.net>]

This is a re-post;  the original seems to have died somewhere!
*******************************
Hi Brian,
I apologize - my statement was hurried and vague - but of serious import.
I was referring to a line of reasoning which I earlier outlined:  the
standard classical line of reasoning (hinging largely on Gauss' law) says
that a conductor (charged or neutral - in an external field or not) is
under a force of tension wherever there is a surface charge.  The net
electrostatic force per unit area (DUE TO THE REST OF THE CONDUCTOR AND
THE REST OF THE UNIVERSE) = (1/2) sigma^2 /epsilon - always an outward
force.  This (says the classical model) is the net electrostatic force
due to the universe, per unit area of charged conductor surface. IE; the
NET ELECTROSTATIC FORCE is not zero - it is outward.  If our scheme says
the conducting surface is in equilibrium under only electrostatic forces,
this (largely Gauss based conclusion) is in question.  I really hope
something is wrong with my reasoning here, because it looks to me like
any classical model has to include some non-electrostatic force to
achieve equilibrium here (as we feel forced to do within the nucleus).
Please straighten me out!

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

-----Original Message-----
From: Brian McInnes <bmcinnes@pnc.com.au>
To: phys-l@atlantis.uwf.edu <phys-l@atlantis.uwf.edu>
Date: Saturday, October 10, 1998 8:59 AM
Subject: Re: IONS/metal pedagogy


> Hi Bob,
>
> ----------
> You wrote
>  The problem is that this raises a perhaps much more
> > serious problem.  If the excess charge on a conducting surface is in
> > equilibrium under only electrostatic forces, then Gauss' law is in
> > trouble.  Again - what do we give up?  Is not the internal field zero?
> > must not a negative surface charge terminate a field line from the
> > outside?  Something of the classical model of a conductor and its
surface
> > must give.  (And this might be the way to go!)
>
> I am probably missing something but I can't see that Gauss' law is in
> trouble.
> As I suggested yesterday and Joseph covered in much more detail today
(times
> are Australian) the surface charges can be in equilibrium under
> electrostatic forces alone as a result of a (small) relocation of
electrons
> in the metal.
> The internal field will be zero.  Agree, because a static situation has
been
> set up.
> There will be field lines terminating on the charges on the surface.
Agree,
> because there will be a field outside the metal.
> But why is Gauss' law in trouble?  What am I missing?
>
> Brian McInnes