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From: DHowell.ES@Xerox.ARPA
Newsgroups: net.physics
Subject: Cancelling EM waves
Message-ID: <543@sri-arpa.ARPA>
Date: Fri, 13-Sep-85 22:49:45 EDT
Article-I.D.: sri-arpa.543
Posted: Fri Sep 13 22:49:45 1985
Date-Received: Sun, 15-Sep-85 12:08:31 EDT
Lines: 22

Here's a new subject to think about, start aguments, etc.

Let's say I have a device that emits an electromagnetic wave.  I put a
certain amount of energy into it, and get most of that energy out as an
electromagnetic wave (the rest being lost to heat in the wires).

Now I set up another one of these, and place it exactly one wavelength
away from the other.  I have them emit in the same direction so that the
waves overlap and are in phase.  Now the output of this system is an
elctromagnetic wave with the same frequency and twice the amplitude.
I'm putting twice as much energy in and getting twice as much energy
out.

Here's the question...  If I place them half a wavelength apart so that
they are 180 degrees out of phase, the waves will cancel.  Now I appear
to be getting no energy out of this system, at least not in the form of
EM waves.  I am still putting as much energy into the system.  All I did
was move one of the devices.  What is happening to the energy?  Is there
an output in another form of energy?  Is it building up in one of the
devices somewhere?

Dan <DHowell@Xerox.ARPA>


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