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Re: POLARIZATION




This touches a question in the exam I'm currently marking. Candidates are
asked to explain why polarization provides evidence for a wave rather than
a particle theory of light. I'm not too thrilled with the question. Is it
possible to explain polarization in terms of photons? Spin is the only
orientable property I can think of.


Leigh replied:
The photon is moving at the speed of light. Only spin orientations
parallel or antiparallel to the direction of motion are allowed.
These two states are polarized (L and R circularly) and degenerate.
Linear combinations are allowed, and these may have any intermediate
polarization state, including all linear states.


So can one account for the phenomenon (of polarization) in terms of the
interactions of spinning photons with the polarizer?

You are correct in disliking the question. It tests no physics
knowledge. It asks for regurgitation of a received factoid. It is
analogous to catechism, and I've tried to avoid teaching
catechism misrepresented as physics.


I think it is factoidal (i.e. an *apparent* fact), but what annoys me is
the way the question invites the student to use the "slit" model beyond
it's useful range, to make a mesh which may or may not catch the
hypothetical particles of light. The best students will know that they are
out on a limb. But I suppose this is more than mere regurgitation.

Mark.


Mark Sylvester
United World College of the Adriatic
34013 Duino TS
Italy.
msylvest@spin.it
tel: +39 40 3739 255