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Re: Simple Radio Signal



I would only emphasize that the separation of the E&M field into near and
far (induction and radiation) is a human, mathematical distinction. This
mathematical distinction is very useful for human modeling, but the
charged particles which respond to the total field couldn't care less!
As always, we must be aware of our reification of mathematical models.

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


----- Original Message -----
From: "John Vanderkooy" <jv@SCIBORG.UWATERLOO.CA>
To: <PHYS-L@lists.nau.edu>
Sent: Tuesday, March 14, 2000 10:39 AM
Subject: Re: Simple Radio Signal


. . .
To truly demonstrate EM waves, we must distinguish them from near-field
induction. A source of EM waves has a near-field and a far-field
region,
demarcated by the condition kr=1, where k is the wave number and r is
the
distance from the source. The result is that for distances less than
lambda/2Pi, the fields have a complicated local dependence, and beyond
that
the fields have the typical 1/r far-field behavior which we associate
with
a radio wave.
. . .
Dr. John Vanderkooy Audio Research Group
http://audiolab.uwaterloo.ca/graphic.html
Tel: 519-885-1211 x 2223 Fax: 519-746-8115
Department of Physics, University of Waterloo
Waterloo ON Canada N2L 3G1