Ans. TOTAL INTERNAL REFLECTION
When the angle of incidence becomes larger than the critical angle, no refraction of light occurs. The entire light is reflected back into the denser medium. This is known as total internal reflection of light.
Explanation: When a ray of light enters from a denser medium to a rare medium, it bends away form the normal (Fig.12.5-a). If the angle of incidence increases, the angle of refraction also increases.
For a particular value of the angle of incidence, the angel of refraction becomes 90° known as critical angle (Fig. 12.5-b). When the angle of incidence becomes greater than the critical angle, no refraction of light occurs. The entire light is reflected back into the denser medium (Fig,12.5-c). This is known as total internal reflection.