= Prism
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= Optical prism
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An <optical prism> is a transparent optical element with nonparallel faces that redirect <light> by <refraction> or <total internal reflection>. For a dispersing prism, the <wavelength> dependence of <refractive index> makes different <wavelengths> leave in different directions.
An entrance slit, collimator, prism and viewing screen or detector form a simple <spectroscope>. A continuous source gives a spread of <colors>, whereas a narrow emission line gives a narrow image of the slit. Rotating the prism changes the deviation; replacing the source while holding the geometry fixed distinguishes a source <optical spectrum> from the prism's dispersive response.
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