Re: funny capacitor

[Bob Sciamanda <trebor@VELOCITY.NET>]

----- Original Message -----
From: "John S. Denker" <jsd@MONMOUTH.COM>
To: <PHYS-L@lists.nau.edu>
Sent: Tuesday, March 06, 2001 04:33 PM
Subject: Re: funny capacitor


> At 02:02 PM 3/6/01 -0500, Bob Sciamanda wrote:
> > . . .
> > Cij which depend only on geometry
> > and the choice of Voltage reference point
>
> The foregoing method of calculation / definition is manifestly
> gauge-invariant.  AFAICT the Cij value depends on geometry and *not* on
any
> choice of gauge.  Can somebody provide an example where a Cij value does
> depend on the gauge?

Consider our old friend the single, isolated conductor and its
description:
Q = C V, where C = C11, the only Cij of this one-conductor system.
Let's make it a sphere of radius a.  Then if V is referred to infinity
C=4*PI*epsilon*a.
OTOH if V is referred to a space-point located  a distance 2a from the
sphere's center, then C=8*PI*epsilon*a.

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