This entry contributed by Kringle Daly

When rays or beams strike a surface and are refracted through the surface they obey Snell's law

where is the index of refraction of the material the incident ray is traveling through, the index of refraction of the material the refracted ray travels through, is the angle of incidence, and is measured between the ray and a line normal to the surface that intersects the surface at the same point as the ray.

Angle of Incidence, Angle of Reflection, Critical Angle, Refraction, Snell's Law