How Everything Works
How Everything Works How Everything Works

Question 625

What material is used in glass to make it polarize light? — FG, Torrance, CA
Actually, the polarizing material you are referring to is a plastic that has been impregnated with iodine atoms. The plastic, polyvinyl alcohol, is heated and stretched to align its long molecules in a particular direction. This plastic is then exposed to iodine, which binds to the long molecules and forms the equivalent of molecular wires along the direction of the aligned plastic molecules. These molecular wires absorb light that is polarized along them because the light's electric field points along its polarization direction and pushes electric charges wastefully along the iodine wires. This light is absorbed and its energy is converted to thermal energy, leaving only light with the other polarization.

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