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Path: utzoo!linus!philabs!cmcl2!lanl!unm-la!unmvax!nmtvax!student
From: student@nmtvax.UUCP
Newsgroups: net.physics
Subject: Re: Cancelling EM waves
Message-ID: <764@nmtvax.UUCP>
Date: Mon, 16-Sep-85 15:25:01 EDT
Article-I.D.: nmtvax.764
Posted: Mon Sep 16 15:25:01 1985
Date-Received: Fri, 20-Sep-85 00:45:10 EDT
References: <>
Reply-To: student@nmtvax.UUCP (Greg Hennessy)
Organization: New Mexico Tech, Socorro
Lines: 30
Summary: 

In article <> DHowell.ES@Xerox.ARPA writes:

>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.

Nope. When you put two of these one wavelength the amplitude does
NOT double. Instead there are twice as many photons emitted, each
photon with energy E = h f where h is Plank's constant and f is
the frequency in Hertz. The waves (photons) will destructively
interfere only along the line of the antennas. At any angle there
will not be complete interference so EM waves will propagate out
with energy happily flowing out of the antennas.

Sincerely;
Greg Hennessy

..ucbvax!unmvax!nmtvax!student


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