Name ______________________________________________ Period _____________

The parallel vertical lines represent light waves striking the surface of a parabolic mirror, and a spherical mirror. These are called incident rays. The short diagonal lines represent the path the light takes after being reflected by the mirror. These are called reflected rays.

1. At the point where each light ray strikes the mirror, draw a line “normal” to the surface.

See green lines in diagram.

2. What do you notice about the angle of the incident light ray and the angle of the reflected light ray?

They are the same angle.

3. Use a ruler or other straight edge to and extend the reflected rays on each diagram. What do you notice?

See diagrams at bottom. I notice that the reflected light rays on the parabolic mirror converge at a single point. I notice that the reflected light rays on the spherical mirror do not converge at a single point. I also notice that the reflected light rays from the spherical mirror do a pretty good job of converging at the same point as long as only the bottom portion of the mirror is considered.

4. What type of mirrors do you think they use when building telescopes? Why?

From class lecture, we learned that spherical mirrors are cheaper to make. And since spherical mirrors do a pretty good job of converging the reflected light rays from the bottom portion of the mirror, I suspect that cheap telescopes use spherical mirrors, while expensive telescopes use parabolic mirrors.

Spherical mirror