Re: pinhole snack question

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From: Paul Doherty (pauld@exploratorium.edu)
Date: Wed Apr 24 2002 - 10:33:45 PDT 

Message-Id: <l03110739b8ec9ba413dc@[192.174.3.125]>
Date: Wed, 24 Apr 2002 10:33:45 -0700
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: pinhole snack question

question 2

The speed of light for light polarized along the direction of stretch for
cellophane tape is slower than the speed of light for light polarized
perpendicular to the stretch.

The difference between the two speeds is also different for each color of
light.

If you put in a light wave polarized at 45 degrees to the stretch the
component of the oscillation along the stretch will move more slowly
through the tape than the component perpendicular. This will cause the
phase of the oscillation to change slowly creating an elliptical
polarization, then a circular polarization, then elliptical again and
finally linear polarization at 90 degrees to the original direction.

The thickness of tape necessary to rotate the polarization by 90 degrees is
different for each different color.

check out the Snack
Polarized Light Mosaic at
http://www.exploratorium.edu/snacks/polarized_mosaic.html

or Paul Hewitt's Conceptual Physics book.

for illustrations.

Paul D

>One of my students built the snack called
>HI TI folks,
>
>One of my students has built the Light Mosaic snack which uses cellophane
>tape to demonstrate the polarization effect. (Light passes through the tape
>and different colors get different angles of polarization. The color
>pattterns it produces are dramatic.)
>
>I have two questions
>
>1) I would like to re-create the snack without using cellophane tape. I
>would like to be able to spray something from an aresol can that would
>produce the same polarizing effect. This will allow a much finer mosaic of
>colors. Does anybody have a suggestion of a spray that is clear and will
>also polarize the light.
>
>2) Is the polarization effect independent of the speed of light effect of
>different colors through a prism. Are these two seperate phenomenon or
>different sides of the same one? (Of course, I realize that Quantum
>Electrodynamics will explain all of these effects but is there a more
>classical explaination that connects these two effects.)
>
>-Mark Lawton
>Portland
>
>_________________________________________________________________
>MSN Photos is the easiest way to share and print your photos:
>http://photos.msn.com/support/worldwide.aspx
>
>
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