From refraction to total internal reflection

1. The angle of the incident light= 0◦.
The angle of refraction = 0◦
2. The angle of the incident light more than 0◦ and less than critical angle θc.
The angle of refraction less than 90◦


3. The angle of the incident light is called the critical angle, θc, when the angle of reflection is 90◦


4. The angle of incident light larger than the critical angle, the refracted ray runs along the surface of the medium. This is called total internal reflection .