Question

Define critical angle. Explain total internal reflection using a neat diagram.

Answer 1

The critical angle is the angle of incidence for which angle of refraction is 90°.
Total internal reflection is the phenomenon that involves the reflection of all the incident light off the boundary. It only takes place when both of the following two conditions are met:

• a light ray is in the more dense medium and approaching the less dense medium.
  
• the angle of incidence for the light ray is greater than the so-called critical angle.