...
Refraction is described by Snell's law, which states that for a given pair of media and a wave with a single frequency, the ratio of the sines of the angle of incidence θ1 and angle of refraction θ2 is equivalent to the ratio of phase velocities (v1 / v2) in the two media, or equivalently, to the opposite ratio of the indices of refraction (n2 / n1):
Common Example:
Going from a medium of lower refractive index, to a medium of higher refractive index, the beam bends toward the normal. In opposite case, when light travels from a higher refractive index to lower refractive index, the beam bends away from the normal.
...