Critical angle
As the angle of incidence is increased, the angle of refraction also increases until it gets closer to 90°. When the angle of refraction is exactly 90° and the light is refracted along the boundary, the angle of incidence has reached the critical angle (C).
In the case that one of the materials (n2 ) is air (which has a refractive index of approximately 1), you can use the following formula to find the critical angle (C):
