Light is a transverse wave, meaning that it oscillates in a direction perpendicular to the
direction in which it is traveling. However, a wave is free to oscillate right and left or up
and down or at any angle between the vertical and horizontal.
Some kinds of crystals have a special property of polarizing light, meaning that they
force light to oscillate only in the direction in which the crystals are aligned. We find this
property in the crystals in Polaroid disks.
The human eye can’t tell the difference between a polarized beam of light and one that
has not been polarized. However, if polarized light passes through a second Polaroid disk,
the light will be dimmed the more that second disk is out of alignment with the first. For
instance, if the first disk is aligned vertically and the second disk is aligned horizontally,
no light will pass through. If the second disk is aligned at a 45º angle to the vertical, half
the light will pass through. If the second disk is also aligned vertically, all the light will
pass through.
Wave Optics on SAT II Physics
SAT II Physics will most likely test your knowledge of wave optics qualitatively. That
makes it doubly important that you understand the physics going on here. It won’t do you
a lot of good if you memorize equations involving d sin but don’t understand when and
why interference patterns occur.