Re: induced emf again

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

Bob Sciamanda wrote:
> the electric field we are
> referring to ( in E =? qVxB) is the field added to the situation by the
> accumulated terminal charges

In the interests of clarity, it might be worth representing
that quantity by some symbol other than E, since it differs
from the E-field that appears in Maxwell's equations.  For
insulators the symbol D is conventional.  For resistive
materials, something like Ebar might serve to represent the
average field, delta_V/L.

> Our E is the field
> whose line integral your voltmeter reads when placed terminal to terminal.

In the presence of changing magnetic fields, that is not
a satisfactory definition.  I can get approximately any
answer imaginable by re-arranging the layout of the leads.

> It is very useful to separate these two E field effects as we have done,
> your analysis is sterile if you don't.

True.

But by the same token, the anaysis is incomplete and does
not make contact with the fundamental physics (which I think
is what the original question was asking for) unless the
relationship between E and Ebar is made explicit.

========================

Also: Ludwik was asking what fields are conservative and what are
not.  It is important to realize that this is !!not!! the same
as asking what fields come from a potential or not.  A  moving
or time-varying potential is not conservative.  This enters the
problem at least twice:
 -- When the wire moves in a magnetic field, the wire itself
is a moving constraint.
 -- The resistive processes (E - Ebar) are time-varying in a
big way.