When the refractive index of the material increases, the extent to which the light beam is refracted on entering the medium also increases, that is, when a light beam enters from a medium of low refractive index to a medium of high refractive index, then the light beam is refracted with a greater extent. The refractive index of the medium depends upon the frequency of light passing through it. Also, each wavelength of light experiences a slightly different degree of refraction. This generally happens when a light beam having different wavelengths of light enters the medium or leaves the medium. The phenomenon of different wavelengths of light being refracted by different degrees is termed dispersion and it is responsible for chromatic aberrations in the objective lens of a microscope.