Get two old (or cheap) pairs of polaroid sun glasses and separate all four lenses from the frames.
Call them A, B, C and D. The order doesn’t matter.
Throw away D. You won’t need it in this experiment.
Line up A and B so you can see a light source (an open window will do fine) through both of them.
Rotate either A or B until the light source can no longer be seen. It is “cancelled out”.
Place C between A and B and the light source once again becomes visible.
Why is that? Adding that extra lens should remove transmitted light, not add some more.
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Welcome to the world of mineral optics
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It was an early researcher of mineral optics that discovered Haidinger's brush....
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It was an early researcher of mineral optics that discovered Haidinger's brush....
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If they are PERFECT polarizers