What Is The Idea Of Total Internal Reflection?

Light can always pass from one medium to an optically denser medium but it cannot always pass into a rarer medium. If the angle of incidence of light in the denser medium is greater than a particular angle (known as the critical angle for that medium), the light is not at all refracted into the rarer medium but is totally reflected. This is known as total internal reflection.

An interesting use of the total internal reflection is in optical fibres, which are fine strands of high quality glass. When light is incident at one end of the fibre, it undergoes repeated total internal reflections and emerges at the other end. Thus, an optical fibre "pipes" light from one point to another. Such optical fibres are used in decorative table lamps. Bundles of tiny optical fibres are used by doctors to see the inside of a patient's stomach. Light is piped down some of the fibres to illuminate the inside of the stomach and is reflected back along some other fibres. This procedure is called endoscopy.