The critical angle is associated with refraction of light This angle is the smallest angle of incidence at which total internal reflection (TIR) occurs
When traveling from an optically denser to optically less dense material, the angle of incidence at which light stops being refracted and is totally reflected
In geometric optics, at a refractive boundary, the smallest angle of incidence at which total internal reflection occurs (188) Note 1: The angle of incidence is measured with respect to the normal at the refractive boundary Note 2: The critical angle is given by
Applies when light strikes a boundary between two materials and the speed of light in the material that it is travelling in is less than the speed of light in the material beyond the boundary If the angle of incidence at the boundary is greater than the critical angle, all the light is reflected