Total internal reflection Total internal reflection is an optical phenomenon. When light crosses materials with different refrective indices, the light beam bends at the boundary surface (i.e., refraction). At a certain angle of incidence (the critical angle C), the light stops crossing the boundary but instead reflects back internally at the boundary surface. This occurs only at a high refractive index/low refractive index boundary, not the other way around. For example it does occur when passing from glass to air, but does not occur when passing from air to glass. At the glass/air boundary what happens depends on the angle (i is the angle of incidence). | i < C | i > C | the ray splits.
Some part of the ray reflects off the boundary,
and some refracts as it passes through. | All of the ray reflects from the boundary.
None passes through. |
This physical property makes diamond so expensive, optical fibre useful and the rainbow in the sky. |