CBSE Class 10 Answered

Total internal reflection is an optical phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than the critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary no light can pass through, so effectively all of the light is reflected. The critical angle is the angle of incidence above which the total internal reflection occurs.
 

The conditions necessary for the phenomena to take place are:

• Light should travel from denser medium to the rarer medium.
• Angle of incidence should be greater than the critical angle in denser medium for a pair of media in contact.