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From: Wasser@cup.portal.com
Newsgroups: sci.misc,sci.physics
Subject: Re: differences between sound and light waves?
Message-ID: <3427@cup.portal.com>
Date: 23 Feb 88 03:57:06 GMT
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The thing to remember when discussing Cerenkov radiation is this:

"c" is the only "magic velocity" that cannot be exceeded (or even attained
by objects which have rest mass.)

Light only travels "at c" in free space.  In water, for instance, light
"travels" at about roughly 0.7 times "c".  Particles being emitted from
decaying nuclides can certainly exceed 0.7 times c.  Charged particles
can be accelerated through a high potential difference at least as high
as 0.9 times c.  So if you have beta particles, for instance, traveling
through water at greater than 0.7c, they set up point disturbances that
spread out to form a cone of radiation, akin to that of a supersonic
object forming a shock cone in the atmosphere.  A large portion of the
cone's energy falls in the visible light range.  Due to the dispersion
effect, different colors of light have different indices of refraction,
and it just so happens that Cerenkov radiation shows up as bluish.  The
half angle of the cone can actually be measured and used to determine
the energy (and thus the speed) of the particle causing it.

That would likely make a physics prof turn green, but, put in simple
words, there is nothing sacred about "the speed of light".  However,
the constant "c" is another story.

Cheers,
Wasser


What Descartes really said was "I Drink, Therefore I Am."
His students quietly changed the quote to read as we know it today.