Ray Diagrams for Mirrors

A useful method to locate images is by geometric construction of a ray diagram. By the judicious choice of rays from the head of the figure, we can quickly locate the image. There are three principal rays that are convevievt to use:

1.) The parallel ray, drawn parallel to the axis. This ray is reflected through the focal point.

2.) The focal ray, drawn through the focal point. This ray is reflected parallel to the axis.

3.) The radial ray, drawn through the center of curvature. This ray strikes the mirror perpendicular to its surface and is thus reflected back on itself.

The intersection of any two rays locates the image point of the head. The third ray can be used to provide a check. Ray diagrams are easier to draw if the mirror is replaced by a straight line that extends as far as necessary to intercept the rays.

Convex mirrors

The central ray heading toward the center of curvature C is perpendicular to the mirror and is reflected back on itself. The parallel ray is reflected as if it came from the focal point F behind the mirror. The focal ray is drawn toward the focal point and would be reflected parallel to the axis.