Re: non-potential voltage

[John Denker <jsd@MONMOUTH.COM>]

On Mon, 17 Apr 2000 14:36:39 -0400, I wrote:

> > . . .
> >Kirchhoff's laws are tantamount to making two simplifying approximations:
> >   a) A capacitor is a two-terminal black box, and there are no significant
> >capacitances outside of capacitors;


At 10:18 PM 4/18/00 -0700, Bob Sciamanda wrote:

> It is not necessary to place this burden on Kirchhof's loop law.  It is
> valid even for non ideal capacitors and inductors;  eg, it even works for
> an open circuit - a highly fringing capacitor situation.

When I spoke of K's laws, I spoke of laws plural (the voltage law *and* the
current law) for a reason.  As I see it, there are two ways to describe
Bob's open circuit:
  1) We blithely ignore the current that flows into the "highly fringing
capacitor situation" (a current that violates K's current law), or
  2) We model the current that flows into this "stray capacitance" by
including in our analysis a "stray capacitor" that doesn't show up in the
fabrication parts list, and has a value that cannot be determined from the
usual sort of circuit diagram.  (This makes K's laws formally correct, but
alas the real physics guarantees that any correct version will be very very
hard to apply in the real world of fringing fields.)

I claim that there is no other way to do it, and that either of these ways
is consistent with my assertions above.