TOTAL INTERNAL REFLECTION

Explanation

Total internal reflection. When a ray of light travels from denser medium to rarer medium, so that angle of incidence is more than critical angle, the ray is totally reflected back in the denser medium. This phenomenon is called total internal reflection.
Consider an object in the denser medium. A ray OA incident on XY bends away from the normal. As the angle of incidence is increased, the angle of refraction goes on increasing. For a certain angle of incidence, the refracted ray becomes parallel to the surface XY or angle of refraction is `90^(@)`. This angle of incidence in the rarer medium for which the angle of refraction is `90^(@)` in the denser medium is called critical angle. When the angle of incidence is further increased, the ray is totally reflected back in the denser medium. This phenomenon is called total internal reflection.

Conditions for total internal reflection
(i) Ray of light must proceed from denser medium to rarer medium, and
(ii) Angle of incidence should be greater than critical angle.
By definition,
`""^(2)mu_(1)=(sin C)/(sin 90)=sin C` or `""^(1)mu_(2)=(1)/(sin C)`