When the two polarizers are set 90 degrees to each other, no light passes through.
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A polarized filter, similar to ones used in polarized sunglasses, only lets light waves through that have their electric field vector oriented along a certain direction. These polarizers, when hit with an unpolarized beam of light, change the light into linearly polarized light by blocking or reflecting everything not aligned along the polarization axis. This means that when two polarized lenses are put one after another at right angles, the light waves let through by one lens can be blocked by the other, meaning that you see no light at all.
- two polarizers
- an unpolarized light beam
Turn on the unpolarized lamp.
Place the first and then the second polarizer in front of the beam and observe how the light appears to change with different combinations.