A GIF Animation
When a ray of light strikes a
plane mirror, the light ray reflects off the mirror. Reflection involves a
change in direction of the light ray. The convention used to express the
direction of a light ray is to indicate the angle which the light ray makes
with a normal drawn to the surface of the mirror. The angle of incidence is the
angle between this normal and the incident ray; the angle of reflection is the
angle between this normal and the reflected ray. According to the law of
reflection, the angle of incidence equals the angle of reflection. These
concepts are illustrated in the animation at the right.