Thursday, July 15, 2010 1:26 PM

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When light strikes the interface between two materials, the light generally divides into two parts: reflected light (angle of incidence=angle of reflection) and refracted light. In order to find the angle of refraction we use Snell's Law.
There is another phenomenon called Total Internal Reflection. This is when the light ray enters the medium at its critical angle. This causes the light to bend such that it travels along the surface. Once the critical angle is exceeded, all the light gets reflected, thus no light gets refracted. This is TIR. Fiber-optic cables use this idea of TIR. The inside of the cable consists of glass while the outer layer is cladding. This is very practical in the field of medicine as we use it in such procedures as colonoscopy.
Total Internal Reflection
When light passes from a medium of longer refractive index into one of smaller refractive index (water to air), the refracted ray bends away from the normal.