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prism





prism
A semi-regular polyhedron constructed from two congruent n-sided polygons and n parallelograms. The word comes from the Greek prizma, which relates to cutting or sawing. A prismoid resembles a prism but has bases that are similar rather than congruent, and sides that are trapezoids rather than parallelograms. An example of a prismoid is the frustum of a pyramid. A prismatoid is a polyhedron with all its vertices lying in two parallel planes.

Prismatic pieces of transparent materials are much used in optical instruments. In spectroscopes and devices for producing monochromatic light, prisms are used to produce dispersion effects, just as Newton first used a triangular prism to reveal that sunlight could be split up to give a spectrum of colors. In binoculars and single-lens reflex cameras reflecting prisms (employing total internal reflection) are used in preference to ordinary mirrors. The Nicol prism is used to produce polarized light.


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   • SOLIDS AND SURFACES
   • OPTIC AND OPTICAL PHENOMENA