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Re: REFRACTION - REFLECTION


On Fri, 09 Jan 1998 8:20 -0600 "Rauber, Joel Phys"
<RAUBERJ@mg.sdstate.edu> writes:

While the answer below is perfectly adequate, I'm not sure I'd want to
use it as an answer to a high school class. Are there any good, more
level appropriate explanations out there?

Joel
----------
From: Dr. William Newbolt
To: QuistO; RAUBERJ; phys-l
Subject: Re: REFRACTION - REFLECTION
Date: Friday, January 09, 1998 8:48AM


In general both refraction and reflection occur at an
interface. You can calculate the intensity of the two
beams using the boundary conditions on electric and
magnetic fields at the boundary of a dielectric and the
angles. At the critical angle it just becomes inpossible
for any of the radiant energy to appear in the refracted
beam and all of it is reflected. You can get this from
boundary conditions, but it is too long and messy to
write out here. See any good E&M book that talks
about the properties of electromagnetic waves. WBN

***********************************************************

Joel's reluctance is understandable. Dr. Newbolt is saying essentially
that internal reflection occurs because we say that it does. When one
sets the boundary conditions of a PDE to behave such-and-such a way, one
should not be surprised that the solution of the PDE corresponds. That
is no answer at all to "Why does this happen?", which cannot be answered,
or "What is the *essential* difference in two different phenomena?". To
say the critical angle was exceeded is to say nothing unless the critical
angle be explained. Why is it critical? The reason one gets internal
reflection is that light and water are magical. Could someone, now, put
that in other words? Perhaps we could pretend that light is waves and
water is stuff. Or that light is particles and water is too. But one
is going to have to cook up an analogy that is fascinating, compelling,
and easily remembered. Perhaps, on the day following the lecture, the
class could be asked, "How many related that explanation to someone
else?"

Regards / Tom