9.4 TOTAL INTERNAL REFLECTION

. TOTAL INTERNAL REFLECTION When light travels from an optically denser medium to a rarer medium at the interface, it is partly reflected back into the same medium and partly refracted to the second medium. This reflection is called the internal reflection. When a ray of light enters from a denser medium to a rarer medium, it bends away from the normal, for example, the ray AO1 B in Fig.

. . The incident ray AO1 is partially reflected (O1C) and partially transmitted (O1B) or refracted, the angle of refraction (r) being larger than the angle of incidence (i). As the angle of incidence increases, so does the angle of refraction, till for the ray AO3, the angle of refraction is /2The refracted ray is bent so much away from the normal that it grazes the surface at the interface between the two media.

This is shown by the ray AO3 D in Fig. . . If the angle of incidence is increased still further (e.g., the ray AO4), refraction is not possible, and the incident ray is totally reflected.