Re: funny capacitor

["John S. Denker" <jsd@MONMOUTH.COM>]

At 04:12 PM 3/10/01 -0500, Bob Sciamanda wrote:
> > To repeat:  There is no God-given grounded shell at
> >"infinity" with respect to which we should measure voltages.
> >There can be an arbitrary gauge(t) at
> > infinity, just like anywhere else
>
> Agreed!

Cool.

> I only need
> a reference point far enough removed from my localized system of
> conductors that changes in the charge distribution of my system are
> undetectable there.

If you had said "want" rather than "need" I would have agreed.  It is OK to
want a distant reference.  Sometimes you might even get it.

But..... having one is not *needed* for doing any sort of physics that I
know about.  The beautiful thing about gauge invariance is that you can
pick *anywhere* as your voltage reference:  near, far, big, little, chassis
ground, earth ground, whatever.




(PS this whole thread is restricted to the low-frequency limit.  If there
are stray time-varying magnetic fields running around, the whole notion of
"ground" goes out the window.  Indeed the whole notion of voltage as a
potential goes out the window.)