Ans. REFLECTION OF LIGHT
When light travelling in a certain medium falls on the surface of another medium, a part of it turns back in the same medium. This is called reflection of light.
Reflection of Light at a Plane Surface
When a ray of light from air along the path OA falls on a plane mirror M, it is reflected along the path OB. The angle of incidence i.e.ZAON represented by i is equal to the angle of reflection i.e. ZNOB represented by r. This is called reflection of light.