We did two labs involving polarization today.  Doc Schuster has a lot of nice videos on optics, here’s his “Intro to Polarization Filters” on youtube.

The first lab we did involved placing a linear polarizer in front of the HeNe laser and measuring the intensity of laser light passing through the polarizer as we rotated the polarizer.  I didn’t have a nice rotation mount, so I just printed out a 360 protractor on cardstock, cut a hole in the middle for the laser to pass thru and put a pointer on the polarizer.  A ‘high tech’ clothes pin was used to hold the polarizer onto the protractor.  This wasn’t the best set up but it worked well enough for the students to see that the intensity varied with the angle.  We used a Texas Instrument sensor (little red box in the photo)that communicates with an iPad via bluetooth to measure the light intensity.  Students found that bumping the setup in any way could seriously effect their results, but they got enough data to show that the intensity depends on the cosine squared of the angle.

The other experiment involved playing with a chunk of calcite.  Previously we had talked about the index of refraction of materials and how it depends on the wavelength of the light.  Different colors of light will move through materials at different speeds and therefore refract more or less, that’s how prisms work and why we have rainbows.  But the index of refraction can also depend on polarization in some materials, like calcite.  Just putting a piece of calcite down on a piece of paper and looking through it you get two images because the light coming from the paper is split into two polarization components with each taking a slightly different path through the crystal.  The students placed the calcite in front of a laser pointer and determined the polarization of the two exiting laser beams were indeed different by 90 degrees.

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