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I Need Polarized Light!
I was sitting in my office and wanted to observe stress in a clear plastic fork. However, I do not have two polarizing filters. I have my polarizing sunglasses but do not want to break them (they are too expensive!)
Given your typical modern office, is there another source of polarized light I can use to observe stress in the plastic fork? (I can think of at least two!)
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Solution
There were several good solutions to this puzzler suggested by readers. I knew there were multiple sources when I posted this puzzler.
One commonly suggested source is a computer LCD monitor. LCD monitors give off polarized light and would make a good source.
There were several variations of using reflected light. Light becomes polarized when it reflects off of a flat surface. People even mentioned using a light source hitting the surface at Brewster's Angle to achieve maximum polarization.
The third technique mentioned was to take advantage of the Sun's polarization band. When sunlight scatters in the sky, you get a band of polarized light 90 degrees from the Sun.
The winner was randomly selected from amongst the correct answers.
I have used all three of these sources of polarized light for demonstrations in a pinch.