# How is the refractive index of a medium related to the speed of light? Obtain an expression for the refractive index of a medium with respect to another in terms of speed of light in these two media?

The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for the light of a given colour and for the given pair of media. This law is also known as Snell’s law of refraction of light. The law follows from the boundary condition that a wave is continuous across a boundary, which requires that the phase of the wave be constant on any given plane.

Refractive Index can be seen as the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values.
n = c/v
Refractive index of one medium in relation to a second medium is given by the ratio of the speed of light In the second medium to speed of light in the first medium.