Two tourmaline crystals act as polaroids, using arc lamp.

• E+45+35

diagram for demo

Some crystals such as tourmaline selectively absorb light rays vibrating in one plane, but not those vibrating in a plane at right angles. When a beam of light is sent through a crystal, the transmitted light is polarized. If a second tourmaline crystal is oriented parallel to the first, then the polarized light is also transmitted by the second. However, if the second crystal is rotated ninety degrees (crossed position), then no light gets through. Two tourmaline crystals used as polarizers, using arc lamp. Ref.: Fundamentals of Physical Optics,-Jenkins & White,1st Ed., p.320

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