## Total Internal Reflection

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When light travels from one medium to another it changes and is refracted. If the light ray is travelling from a less dense to a more dense medium, it is refracted towards the and if it is travelling from a dense to less dense medium it is refracted from the normal.

For total internal reflection to occur the light must travel from a medium to a less dense medium e.g. glass to air.
As the angle of incidence increases so does the angle of . When the angle of reaches a value known as the critical angle the refracted ray travels along the surface of the medium, or in other words it is refracted to an angle of 90o. In glass, the angle for the angle of incidence is 42o.

When the angle of incidence of the light ray is than the critical angle then no refraction takes place.
Instead, all the light is back into the denser material, in this case the glass. This is called internal reflection.