TOTAL INTERNAL REFLECTION
When light enters from one medium to the another with different optical density, the direction of light ray changes at the point of intersection between two mediums due to refraction
When light ray enters from a denser medium to a rarer medium it bend away from the normal (as shown in figure 1). As the angle of incidence increases the refracted ray moves further away from normal.
At a particular angle of incidence, the refracted ray passes through the plane of intersection between two medium, this angle of incidence is known as critical angle(as shown in figure 2).
If the angle of incidence is greater then the critical angle, refraction doesn’t occurs and all the light rays will be reflected back to the same medium. This is known as total internal reflection