When light is reflected by a mirror, the angle of incidence is always

When mirror reflects a ray of light, the angle of incidence is always equal to the angle of reflection ( ∠i= ∠r).

When ray of light falls on a reflecting surface, it is sent back by that surface. This is called reflection of light. The light ray falling on the surface is the incident ray whereas the ray reflected by the surface is called reflected ray.

When a line is drawn (at the point of incident ray) perpendicular to the plane of mirror, the angle formed by incident ray with the normal (perpendicular line) is called angle of incidence and the angle formed by the ray that is reflected is called angle of reflection.

As per the second law of reflection-  

Angle of incidence is always equivalent to the reflected angle.    

∠i= ∠r