Spherical Mirrors: concave and convex mirrors. Today’s agenda: Plane Mirrors. You must be able to draw ray diagrams for plane mirrors, and be able to calculate image and object heights, distances, and magnifications. Spherical Mirrors: concave and convex mirrors. You must understand the differences between these two kinds of mirrors, be able to draw ray diagrams for both kinds of mirrors, and be able to solve the mirror equation for both kinds of mirrors.

Mirrors Images Formed by Plane Mirrors Plane mirrors form virtual images; no light actually comes from the image. The solid red rays show the actual light path after reflection; the dashed black rays show the perceived light path.

*The object distance and image distance are equal: s=-s’. These do not appear to be on your starting equation sheet, but they really are! Just use the mirror equation (coming soon) with f=. y y’ s s’ *The object distance and image distance are equal: s=-s’. The object height and image height are equal: y=y’. The magnification of a plane mirror is therefore one. The image is upright and virtual. The image is reversed front-to-back relative to the object. *The – sign is needed because of sign conventions that go with the mirror equation—see later.

Example: how tall must a full-length mirror be? A light ray from the top of your head reflects directly back from the top of the mirror.

y/2    y/2 s s’ To reach your eye, a light ray from your foot must reflect halfway up the mirror (because I = R = ).

The mirror needs to be only half as tall as you.    y/2 s s’ The mirror needs to be only half as tall as you. This calculation assumed your eyes are at the top of your head.

Example: where is the image located (top view)?

Example: distant object in a small mirror. Find some similar triangles! (Only one is fully shown in the figure.) The last time I tried to do this, the object was too big to “fit in” the mirror, and my head got in the way.