Applications of Total internal reflection
Total internal reflection is the main cause of the brilliance of diamonds. The refractive index of diamond with respect to air is 2.42. Its critical angle is 24.41o. When light enters diamond from any face at an angle greater than 24.41o it undergoes total internal reflection. By cutting the diamond suitably, multiple internal reflections can be made to occur.
(ii) Optical fibres
The total internal reflection is the basic principle of optical fibre. An optical fibre is a very
thin fibre made of glass or quartz having radius of the order of micrometer (10?6m). A bundle, of
such thin fibres forms a ?light pipe? (Fig.a).
Fig. b shows the principle of light transmission inside an optical fibre. The refractive index of the material of the core is higher than that of the cladding. When the light is incident at one end of the fibre at a small angle, the light passes inside, undergoes repeated total internal reflections along the fibre and finally comes out. The angle of incidence is always larger than the critical angle of the core material with respect to its cladding. Even if the fibre is bent or twisted, the light can easily travel through the fibre.
Light pipes are used in medical and optical examination. They are also used to transmit communication signals.