Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Surface Charges and Feedback in Simple Circuits



Having read Preyer's preprint, I now conclude he is modelling an RC
discharge but has chosen an RC decay time of several nanoseconds and
propagation time (d/c) and decay time (pho*epsilon) of the order of
picoseconds. His simulations go only to about 150 picoseconds and so
never approach a static equilibrium - a well defined, "slowly" decaying
current is still flowing - the "intermediate state" which you correctly
inferred (exponential decay).

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor
----- Original Message -----
From: "John S. Denker" <jsd@MONMOUTH.COM>
To: <PHYS-L@lists.nau.edu>
Sent: Saturday, February 16, 2002 3:46 PM
Subject: Re: Surface Charges and Feedback in Simple Circuits


Bob Sciamanda wrote:

I think his algorithm, in effect, treats the capacitor as if it were a
battery. His imposition of J=sigma*E inside the conductors ( and I
suppose
inside the capacitor) forces a current flow.

OK. Then it's not as crazy as I thought.
Just poorly expressed.
After all, a battery can be thought of as a
reeeeally high-capacitance capacitor.
This must be a severely overdamped RLC circuit.

What Preyer calls "steady state" should be reworded
as an _intermediate_ timescale (tau). Some things have
happened on a time scale much shorter than tau, such as
relaxation of the current pattern, radiation, inductive
effects, et cetera. But RC relaxation (i.e. discharge of
the battery) happens on a timescale much longer than tau.

And then I'm not sure that this scenario should be
called "the simplest circuit". This is several steps
removed from utmost simplicity, IMHO.