Heat is also generated as a by product. Mirrors are specular devices that can change the direction a light beam. Polished on the specular surface causes regular reflection and the image of the luminous source is sharply defined. A plane mirror of the plate glass is silvered on one surface to reflect the light efficiently. When a ray enters the dense medium at an oblique angle.
Refraction does occur and the ray is bent toward normal.
The density of a material is determined by the speed of light through the material. This effect is termed total internal reflection. The minimum angle at which total internal reflection occurs is called the critical angle. It can calculated by assuming the angle of refraction is 90 such that refracted light is directed along the interface. For the derivation, we will use Huygens principle.