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Re: Fields

I often illustrate our different meanings of the word "interference" by
considering (or demonstrating) two intersecting flashlight (or laser) beams,
each illuminating its own screen. By observing only one of the screens, one
cannot tell whether the other flashlight is on or off. Then contrast this
with the same experiment using machine guns (particle, instead of wave,
generators) in place of the flashlights. I encourage the use of the word
"superposition" wherever the optics texts speak of the "interference" of
waves.

It is curious that we have never been conditioned to speak of the
"interference" of forces whose effects superimpose; the parallel is exact.

For the nit-pickers: there are higher order QED genuine interference
effects between photons.

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

-----Original Message-----
From: Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>
To: PHYS-L@LISTS.NAU.EDU <PHYS-L@LISTS.NAU.EDU>
Date: Thursday, February 04, 1999 11:40 AM
Subject: Re: Fields


We all know what happens. But for the argument's sake let me
disagree with Philip's reply to Jim (see below).

If A interacts with B then some change in B must occur. That is
my definition of interaction. The superposition principle does not
imply the interaction of two fields, it only states that the
contribution
of one field to what we observe is not changed by the presence or
absence of another field. Thus, in classical physics, electric fields
do not interact.
Ludwik Kowalski
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Does it make any sense to say something like one electric field
interacts with another?
Jim Green

Sounds imprecise, but not wrong. Force fields interact in the
sense that they are vector fields, so electric fields add like
vectors
at any given point in space. Thus, electric fields from multiple
sources can reinforce or cancel each other at any given point in
space.
Philip
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