The Law of Reflection

A GIF Animation

When a ray of light strikes a plane mirror, the light ray reflects off the mirror. There is a change in direction of the light ray. We use a number of different terms to describe such a reflection.  The ray going from the laser to the mirror is termed the incident ray (remember going in), while the ray bouncing off the mirror is appropriately called the reflected ray (it reflects). There is also the line which is always 90 degrees from the surface of the mirror, called the normal line.

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:

angle of incidence = the angle of reflection

These concepts are illustrated in the animation at the right.

This page was modified by J.T. Schemm of Newton North High School

Comments and suggestions can be sent by e-mail to J.T. Schemm

This page last updated on 6/8/98.