C'mon, John. I think it's perfectly clear that the electric field we are
referring to ( in E =? qVxB) is the field added to the situation by the
accumulated terminal charges - sure, the retarding force is due to the E
field of lattice ions (ie; collisions with the lattice). Those fields are
always there and are cancelled on a macroscopic scale. Our E is the field
whose line integral your voltmeter reads when placed terminal to terminal.
It is very useful to separate these two E field effects as we have done,
your analysis is sterile if you don't. Your E field is zero in an
external resistor. Our E field is non zero and has a line integral equal
to IR and can cause currents in an externally applied voltmeter.
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: Sunday, May 05, 2002 12:03 PM
Subject: Re: induced emf again
| I wrote:
| > | When E is equal to v × B, that
| > | is the condition for zero net force on the electrons. Any
| > | steady straight-line current meets this condition, whether
| > | the current is zero or not, and whether the resistance is
| > | zero or not.
|
|
| Bob Sciamanda replied:
| >
| > Yes the net force is zero, but if there is resistance one of the
forces is
| > a retarding force. Consider the limit when this retarding force
becomes
| > irresistible (the rod is an insulator). Then no charges move or
| > accumulate; no E is established; yet qVxB still operates - balanced
| > completely by the retarding force.
|
| I agree with all that except the word "but". I don't see
| how any of that is inconsistent with what I've been saying.
|
| The retarding force must come from an E field, right?
|
| I haven't seen the Lorentz force law written in terms of
| q E + q v × B + retarding_forces
| I think it's just
| q E + q v × B
|
| It may require extra effort to measure the E field associated
| with an insulator, but it can be done. The following returns
| over 250 hits:
| http://www.google.com/search?q=electric+field-mill+measure
|