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Path: utzoo!linus!philabs!cmcl2!harvard!talcott!gjk
From: gjk@talcott.UUCP (John)
Newsgroups: net.physics
Subject: Re: Cancelling EM waves
Message-ID: <509@talcott.UUCP>
Date: Wed, 18-Sep-85 10:59:34 EDT
Article-I.D.: talcott.509
Posted: Wed Sep 18 10:59:34 1985
Date-Received: Sat, 21-Sep-85 11:17:19 EDT
References: <543@sri-arpa.ARPA> <542@petrus.UUCP>
Organization: Harvard
Lines: 20
Keywords: lasers

In article <542@petrus.UUCP>, mwg@petrus.UUCP (Mark Garrett) writes:
> > Here's the question...  If I place [two identicle electromagnetic sources
> > operating at some frequency] half a wavelength apart so that
> > they are 180 degrees out of phase, the waves will cancel.
...
> > Dan <DHowell@Xerox.ARPA>
> 
> The key is to think of the problem in three (or even two) dimensions.
> True, along the line passing through the two points, you will have 
> exactly canceled the transmission; and also at certain points in the
> plane or space.  But generally, there will be regions of destructive
> interference and of constructive interference...

Yes, this might happen with an antenna, but it certainly wouldn't happen with
a laser.  For an explanation of what happens when you do this experiment with
lasers or other planar (as opposed to spherical) light sources, see my other
posting.
-- 
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