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Re: REFRACTION - REFLECTION




Hmm... would it be more understandable to argue that the parallel
component of each photon's momentum has to stay the same as they
cross the boundary, and that above a certain angle that's not
possible?

-steve

"Thomas" == Thomas L Wayburn <twayburn@juno.com> writes:

Thomas> On Fri, 09 Jan 1998 8:20 -0600 "Rauber, Joel Phys"
Thomas> <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

Thomas> ***********************************************************

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

Thomas> Regards / Tom