19.1  Mirrors (continued)

The Law of Reflection

Optics includes the study of how mirrors and lenses form images. In your study of optics, assume that light is made up of rays that travel in straight lines. A ray diagram shows how rays change direction when they strike mirrors and pass through lenses.

Figure 1 shows a simple ray diagram of the law of reflection. The incoming ray, called the incident ray, approaches the mirror. The angle of incidence is the angle the incident ray makes with a line drawn perpendicular to the surface of the mirror. The mirror reflects the incident ray. The angle of reflection is the angle the reflected ray makes with the perpendicular line.   The law of reflection states that the angle of reflection is equal to the angle of incidence.

Figure 1  The flat (plane) mirror and the mirror-like lake surface both obey the law of reflection. According to the law of reflection, the angle of an incident ray equals the angle of the reflected ray.

Next time you are in a car behind a large truck, look for a sign that reads, “If you can't see my mirror, then I can't see you.” Light travels from you to the mirror to the driver's eyes and also from the driver to the mirror to your eyes. If you do not have a line of vision to the truck's side-view mirror, then the truck driver does not have a line of vision to you. It can be dangerous to drive too close to large trucks!

For: Links on mirrors