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Re: non-potential voltage

Until John convinces me otherwise (and he often finally does), I'm agreeing
with Bob.


1) 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.

2) At 08:22 AM 4/19/00 -0400, Bob Sciamanda also wrote:

Stating K's current law in the familiar form: "In steady
state, the net
current into any point is zero", this is simply a statement
of charge
conservation and applies even to volume current distributions. It is
inapplicable only during the transient startup when (mostly)
surface charge
distributions are being established to drive the steady
state current.

And is still applicable in transient phases if you allow displacement
current to be included in the use of K current law.


If "steady state" means DC, then K's law has nothing to say about
capacitors of any kind, or about fringing fields, and is not
very useful.

John, I'm not sure if I know what you mean by fringing field in this
context. OTOH I assume you mean that steady state DC won't describe anything
other than a fully charged capacitor when "no" current is being "driven
through it"; i.e. all of time is a transient porting for DC currents into a
capacitor. (do I get your drift, here??)


If "steady state" includes "steady" AC signals, then
statement 2 is false
in context. Because of the fringing fields, there is a
nonzero AC current
into the node which Bob calls an "open circuit". The real
physics violates
Kirchhoff's assumptions.

I'd repeat here the comment about displacement current.


I renew the assertion that as applied to ordinary circuits,
Kirchhoff's
laws are tantamount to assuming that circuit elements are
black boxes, and
that there are no significant electric fields outside of
"capacitor" black
boxes, and no significant magnetic fields outside of "inductor or
transformer" black boxes.