prism

prism in optics, a piece of translucent glass or crystal used to form a spectrum of light separated according to colors. Its cross section is usually triangular. The light becomes separated because different wavelengths or frequencies are refracted (bent) by different amounts as they enter the prism obliquely and again as they leave it (see refraction ). The shorter wavelengths, toward the blue or violet end of the spectrum, are refracted by the greatest amount; the longer wavelengths, toward the red end, are refracted the least. The Nicol prism is a special type of prism made of calcite; it is used for polarization of light .

prism A solid block of glass or other transparent substance, with at least two flat faces inclined to each other at an angle called the refracting angle. The intersection of these two faces is called the edge of the prism, and the cross-section at right angles to the edge is known as the prism's principal section. The main use of prisms in astronomy is to disperse light into a spectrum for spectroscopy; they are also used in binoculars to fold the light path. See also porro prism; roof prism.