Refraction is the bending of a wave when it enters a medium where its speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media. The amount of bending depends on the indices of refraction (defined as the speed of light in vacuum divided by the speed of light in the medium) of the two media and is described quantitatively by Snell's Law.
As the speed of light is reduced in the slower medium, the wavelength is shortened proportionately. The frequency is unchanged; it is a characteristic of the source of the light and unaffected by medium changes.
Credits: Dr. Rod Nave
Snell's law
Credits: 7activestudio