5CH - Critical angle and internal reflection

Not all light will be refracted through materials such as glass. Materials like glass have the ability to internally reflect light if the ray is at a certain angle. This is called the critical angle and is the angle beyond which no refraction will take place. In other words, the light will not pass through the material but be reflected back in the original direction of the ray.

Remember that at the precise point of the critical angle, the ray of light refracts into the air at 90 degrees. This is the last refraction that occurs before all light is reflected. Recall also that the angle of incidence is always equal to the angle of reflection.