Law of reflection

A ray diagram showing angle of incidence and angle of reflection.A ray diagram for reflection at a mirror
  • the hatched vertical line on the left represents the plane mirror;
  • the dashed line is called the normal, drawn at 90° to the surface of the mirror;
  • the angle of incidence, i, is the angle between the normal and incident ray;
  • the angle of reflection, r, is the angle between the normal and reflected ray.
A ray diagram showing light rays coming from an object, reflecting at the surface normal of a plane mirror. the angles of incidence and the angles of reflection are also highlighted.

The law of reflection states that: angle of incidence i = angle of reflection r.

For example, if a light ray hits a surface with an angle of incidence of 45°, it will be reflected with an angle of reflection of 45°.