Re: "Faraday's Final Riddle"

[Bob Sciamanda <trebor@VELOCITY.NET>]

I don't like to be a "flamer" but this paper propagates the pernicious
idea (common in engineering circles) that Faraday induction results from
the "cutting of magnetic field lines" by a conductor.  (another bastard
offspring of the reification of static fields).

The correct, basic physics is that Faraday induced emfs result from:

1) the Q*VxB force of a magnetic field on a moving charge (called "the
generator principle" when Q is a conduction electron in a moving wire),
and/or

2) the electric field which is sourced by a time changing magnetic field,
as described by Curl E = -dB/dt.

1) requires that (in the observer's frame) a conductor is moving where
there exists a magnetic field;
2) requires that (in the observer's frame) the magnetic field vector is
changing in time at some fixed space positions.
"Cutting B lines" has nothing to do with anything and leads only to
confusion.

Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

"This paper gives wrong solutions to trivial problems. The basic error,
however, is not new."
Truesdell, Clifford, Mathematical Reviews 12, p561.


----- Original Message -----
From: brian whatcott <inet@INTELLISYS.NET>
To: <PHYS-L@lists.nau.edu>
Sent: Sunday, October 03, 1999 11:49 PM
Subject: "Faraday's Final Riddle"


> Thought you might be interested.
> I recalled a recent thread on homopolar generators et al when I saw
> a reference to a paper written for the Institute of Engineers, Ireland.
>
>  http://www.iei.ie/papers/faraday1.html
>
> Why is spinning a disk in an axial field different from spinning an
> axial field magnet - and why does spinning a field and a disk
> together produce unexpected effects?