TOTAL INTERNAL REFLECTION

Total internal reflection can occur when light travels between two media from the medium with the higher refractive index into the medium with the lower index of refraction. There is a critical incident angle at which Snell's law predicts the refracted angle will be 90 degrees. At incident angles greater than this critical angle, light can not be refracted into the medium with the lower refractive index. Hence all the light striking the surface must be reflected. We have total internal reflection. The critical angle is given by the formula: sin(theta critical)=(n2/n1), where n1 is the larger refractive index and n2 is the smaller.

Total internal reflection can only occur when light is trying to travel from a material with a high refractive index into one with a lower refractive index. It will not occur when traveling from a low refractive index to a higher refractive index. For example, light traveling from glass to air might experience total internal reflection, but light traveling from air to glass never will. The greater the difference in refractive index between the two materials, the more likely there will be total internal reflection.

Fiber optic cables use total internal reflection inside the optical fiber. The light enters the optical fiber, and every time it strikes the edge of the fiber it experiences total internal reflection. This way the light travels down the length of the optical fiber.

Binoculars and other optical instruments often use prisms to reflect light. The light enters the prism in such a way that it will strike the other side of the prism and be totally internally reflected. The prism can in this way act as a mirror.

Rainbows form when light enters raindrops. The light is totally internally reflected inside the raindrop before leaving. In addition the light of different colors is refracted at different angles to separate the colors in an effect called dispersion.

The brilliance of diamonds results from light entering the diamond and being totally internally reflected from the opposite side before exiting in approximately the original direction.




source
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