# prism

A right three-side prism (left) and oblique prism (right).

When light hits a prism it is refracted by the two surface it hits (1, 2). White light splits into the spectrum (3) because each of the colors of the spectrum have varying wavelengths. For example, the short wavelengths of blue and indigo are refracted more than the colors further down the spectrum with longer wavelengths such as orange and red.

In mathematics, a prism is a polyhedron constructed from
two congruent *n*-sided polygons and *n* parallelograms. The word 'prism' comes from the Greek *prizma*, which relates
to cutting or sawing. A prism is a semiregular polyhedron if all of its faces are regular polygons. If the lateral surfaces of the prism are perpendicular to the base, it is said to be a **right prism**; otherwise, it is known as a **oblique prism**.

If the base of a prism is a regular *n*-agon, it is said to be a regular *n*-sided prism. The distance between the base and the upper surface is called the altitude. The volume of a prism with base-area *B* and altitude *h* is *V* = *B*.*h*.

A four-sided right prism is also called a **right parallelepiped**. A right parallelepiped whose altitude is equal to the edges of the base is a cube. A four-sided oblique prism is also called a parallelepiped. Prisms with equal altitudes have equal volumes.

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.

## Optical prisms

In physics, 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.