Polarization of Light
Charles Brass, Instructor
Antonio Wood, TA

Light waves, like all electromagnetic waves, are transverse waves. But unlike a simple transverse wave that travels up and down, light waves vibrate in many different directions. Some vibrations are up and down, some are side to side, and others are vibrating at many of the angles in-between. So, when you think of the direction of a transverse wave, you probably think of this:

However, as we begin to understand the polarization of light, you need to think of the transverse light waves travelling in many directions like this:

Now, let’s visualize a time when this may be problematic. Let’s say that you are on the shore of a lovely Geneva Lake here in Williams Bay. (Doing water wave observations, of course.) But the glare from the lake makes you squint. No problem, you pull out your brand new sun specs that happen to have polarized lenses. On they go, and you can enjoy the lovely vista. What happened?

The glare as it is reflected from the lake is polarized in a horizontal direction. Your sunglasses have vertical polarizing filters in the lenses. These block the horizontal rays of the glare. However, the rest of the light is not polarized so all of the other light waves that are vertically vibrating pass through with no problem.

A polarizing filter is constructed with many parallel vertical or horizontal slits. When light passes through the filters, only the light that vibrates in the same direction as the slits can pass through the filter. When a vertical polarizing filter is placed in front of light rays, only the vertical vibrating waves get through. If the filter is than rotated 90o, it will block the all of the remaining waves that are not vibrating horizontally.

During our exploration time, we will analyze the plane of polarization of polarizing filters. We will also do some photoelastic stress activities.

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