Physics 2000 Science Trek Polarization

Blocking Light

The easiest way to understand how a polarizing filter affects the components of an electromagnetic wave is to try it yourself. In the experiment below, use the switches to first put only one lens in the path of the light. Twist the lens around and observe the image of the lightbulb on the camera.

But I don't notice a difference at all!

That's because our eyes can't really tell the difference between light that is vertically polarized and light that is horizontally polarized. In fact, we can't really distinguish between unpolarized and polarized light at all. Now add the other two filters and see what happens when all three are present.

Zoom in to see what a hydrocarbon molecule does as it absorbs light.

This is so cool! I can take the filter out of the middle and block the light from the camera's view with the remaining filters. When I put the middle filter back in, everything changes! If the middle filter is aligned with either of the two filters, the camera still doesn't see any light. If I put the middle filter in so that it's not aligned with either of the other lenses, some light gets through. The most light gets through if I turn the middle lens so that it's at a 45 degree angle to both of the other lenses.

Can you try to explain why this happens?

When the middle filter was out, I could adjust the last filter so that it absorbed all of the light that emerged from the first filter. If I put the middle filter in so that it was aligned with either of the other two filters, all of the light was still absorbed. If I put the middle filter in at another angle, it only absorbed part of the light from the first filter. This allowed some components of the light to pass through the final filter. Adding the middle filter caused the polarized light to no longer be completely parallel to the strands of molecules in the final filter.

You are absolutely right! Now we can take a look at how light can be manipulated by using many lenses.

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