Re: volume polarization vs. surface charge

[Bob Sciamanda <trebor@VELOCITY.NET>]

-----Original Message-----
From: John S. Denker <jsd@MONMOUTH.COM>
To: PHYS-L@LISTS.NAU.EDU <PHYS-L@LISTS.NAU.EDU>
Date: Friday, March 05, 1999 6:10 AM
Subject: Re: volume polarization vs. surface charge


> . . .if you count *real* electrons and
> *real* protons in a small volume encompassing the surface of a polarized
> dielectric, there is a mismatch.  There has never been a charge that is
> more real, more non-fictitious.
> . . .

It is common pedagogical practice to arrive at the notion of bound charges
by using the specific dipole model of end to end pos and neg charges (just
as we do in modeling a bar magnet as two separated monopoles).  This model
indeed leads to the visualization of  layers of real charge ("real protons
and real electrons") laid bare at opposite surfaces of a polarized
dielectric.

I merely point out that the bound charge notion does not rest on this or any
other particular dipole model;  it refers only to the dipole moment of the
molecular charge distribution, whatever its geometric details  (it may also
have moments of higher order).

Also, bound charge is not restricted to surfaces (only in the case of a
uniformly polarized dielectric);  wherever there is a divergence of the
polarization volume density, an equivalent bound monopole charge density can
be used to calculate (the dipole approximation of) the field of the
polarized matter.

> . . .
> Suggestion:  Let's try to be explicit about which viewpoint is being taken,
> and let's try to be tolerant of other viewpoints as long as they get the
> right answer.


AMEN!

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