I would appreciate if somebody could comment on the following
observations. Both are from today's lab.
1) Students in my Optics class were analyzing the beam of light
reflected from plexiglas at the Brewster angle. Pasco Incandescent
Light source, Pasco Light Probe and Pasco Polarizer were essential
instruments. The reflected light intensity varied only by the factor
of 6 when the polarizer was turned from the maximum orientation to
the minimal orientation. Practically the same result was obtained at the
reflection angle about 7 degrees away from Brewster. Why is the
extinction ratio, Imax/Imin, so small? I expected it to be at least 20
(on
the basis what the eye sees when two Pasco films are cross-oriented.)
2) The plexiglas was replaced by the aluminum foil (mirror) and the
beam reflected at 50 degrees was again analyzed for linear polarization.
I expected Imax/Imin ratio to be 1.0, the measured value turned out to
be
very close to 1.4. How can polarization from a metal be explained? Why
is the extinction ratio so small? Should it be the same for all metals?