Waves are refracted at a boundary between different materials. Any waves may be refracted. The waves change direction, as shown in the diagrams below. When passing from a medium to a 'denser medium', waves are refracted towards the normal. Conversely, when passing from a medium to a 'less dense' medium, waves are refracted away from the normal.
Refraction For Light Rays
Refraction is governed by Snell's Law. If
is the refractive index of the second medium relative to the first then
Where
and
are the wavelengths before and after refraction and
and
are the speeds of the waves before and after refraction respectively. The frequency does not change on refraction.