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From: przemek@gondor.cs.psu.edu (Przemyslaw Klosowski)
Newsgroups: sci.misc,sci.physics
Subject: Re: differences between sound and light waves?
Keywords: macroscopic behaviour
Message-ID: <3312@psuvax1.psu.edu>
Date: 22 Feb 88 01:29:19 GMT
References: <413@prlb2.UUCP> <4110@aw.sei.cmu.edu> <6917@agate.BERKELEY.EDU> <4809@ihlpg.ATT.COM> <1181@microsoft.UUCP>
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Reply-To: przemek@gondor.cs.psu.edu (Przemyslaw Klosowski)
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In article <1181@microsoft.UUCP> t-peterw@forward.UUCP (PUT YOUR NAME HERE) writes:
>>There is analogous light behavior.  It's called Cherenkov radiation.
>>It occurs when particles travel through a transparent medium faster
>>than the speed of light in that medium.  It occurs in the everyday
>>world, but not so as you'd notice.
>>-- 
>>Bill Tanenbaum 
>
>As far as I know the only thing that travels faster than the speed of
>light is the Starship Enterprise. As a high school student, I spent a summer
>
>Please correct me if I should err.
	^^^^^^^^^^^^^^^^^^^^^^^^^^
>Peter Williams         University of Waterloo coops like to move, and move,

 OK here it is. The speed of light IN VACUUM (c) is indeed a fundamental barrier
nott to be taken lightly (unlike '55 mile limit'). Now in the dielectric
medium (everything that contains atoms is dielectric) EM wave interactions
with the electrons in an atom cause those electrons to vibrate and emit
their own EM radiation. This radiation sums with initial wave and changes
its phase continuously. It looks like the total wave slows down a fraction
of a wavelength each cycle, and travels with a speed of c/n (n is the 
refractive index). You can calculate n based on the parameters of the 
electrons (simple case is to assume that electrons are free wrt atoms---this
is plasma). Now nothing prevents charged particle from travelling in this
dielectric with speed greater than c/n (but OF COURSE smaller than c). 
This is when Cerenkov radiation sets in---how does it do it is another story.

Your reactor sages were right: EM radiation cannot travel faster than the 
speed of light (EM radiation itself) in the medium. In fact it travels with
its own speed all right :^)


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