Question

what is critical angle in total internal reflection? ​

Answer 1

Total internal reflection takes place when the angle of incidence for the light ray is greater than the so-called critical angle. The critical angle is defined as the angle of incidence that provides an angle of refraction of 90-degrees.

Answer 2

The critical angle is the angle of incidence beyond which rays of light passing through a denser medium to the surface of a less dense medium are no longer refracted but totally reflected. It is the smallest angle of incidence that yields total reflection.