(i) Name the phenomenon on which the working of an optical fiber is based.
(ii) What are the necessary conditions for this phenomenon to occur?
(iii) Draw a labelled diagram of an optical fiber and show how light propagates through the optical fiber using this phenomenon.

(i) Optical fiber works on the principle of Total internal reflection of light rays. When the incident angle is greater than the critical angle, the rays are reflected continuously inside the cavity of the optical fiber.

(ii) The necessary conditions for total internal reflection are:

(a)The angle of incidence should be greater than the critical angle for the media.

(b) Light should travel from a denser medium to a rarer medium.

(iii) An optical fiber consists of a core made of glass or silica or any material with high refractive index and a cladding whose refractive index is less than that of core. When a light ray of angle of incidence greater than the critical angle enters through the core, it suffered total internal reflection at the core cladding interface. Then as it moves, it strikes the opposite side with again the angle of incidence greater than the critical angle. In this way, a ray of light bounces from interface within the core, each time suffering a total internal reflection till it emerges out of the optical fiber.