3.21 explain the meaning of critical angle c

Critical Angle:

• The angle of incidence which produces an angle of refraction of 90⁰ (refracted ray is along the boundary of the surface).
• When the angle of incidence is greater than the critical angle, total internal reflection occurs (all light is reflected at the boundary).
• This effect only occurs at a boundary from a high refractive index material to a low refractive index material.