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The refractive index of materials varies with the wavelength (and frequency) of light. This is called dispersion and causes prisms to divide white light into its constituent spectral colors, and explains how rainbows are formed. As the refractive index varies with wavelength, according to Snell's law, so will the refraction angle as light goes from one material to another. This makes different colors go in different directions.
In optics, *dispersion* is the phenomenon in which the phase velocity of a wave depends on its frequency,^\[1\]^ or alternatively when the group velocity depends on the frequency. The *refractive index* of materials varies with the wavelength (and frequency) of light.
Media having such a property are termed _dispersive media_. Dispersion is sometimes called *{_}chromatic{_}{*}* dispersion* to emphasize its wavelength-dependent nature, or *group-velocity dispersion* (*GVD*) to emphasize the role of the group velocity.
Dispersion is most often described for&nbsp;light&nbsp;waves, but it may occur for any kind of wave that interacts with a medium or passes through an inhomogeneous geometry (e.g., a&nbsp;[<span style="color: #0b0080">waveguide</span>|http://en.wikipedia.org/wiki/Waveguide]), such as&nbsp;sound&nbsp;waves
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Fig 01: A&nbsp;dispersive prism, material dispersion (a&nbsp;[<span style="color: #0b0080">wavelength</span>|http://en.wikipedia.org/wiki/Wavelength]\-dependent [<span style="color: #0b0080">refractive index</span>|http://en.wikipedia.org/wiki/Refractive_index]) causes different colors to [<span style="color: #0b0080">refract</span>|http://en.wikipedia.org/wiki/Refraction]&nbsp;at different angles, splitting white light into a&nbsp;[<span style="color: #0b0080">rainbow</span>|http://en.wikipedia.org/wiki/Rainbow].