The index of refraction of a particular medium is nearly the same for all wavelengths hence we often associate a single value the average value of the index of refraction to the medium. There is nevertheless some variation in the value of the index of refraction with wavelength. Thus the angle of refraction that occurs when light enters or exits such a medium is slightly different for different wavelengths of visible light. What is the name of this phenomenon?

Ans:

The dispersion of light is the scattering out of light and that is exactly what occurs when the colours that make up white light are split up by a prism as a result of the slight dependence of the index of refraction of a transparent medium on the wavelength of the light.