Plane Mirrors

Mirrors are usually made of a sheet of glass that is coated with a thin layer of shiny metal on one surface. A mirror with a flat surface is a plane mirror. The large mirror in your bathroom is a plane mirror. When you look into a plane mirror, you see your reversed reflection—a right-left reversed image of yourself. An image is a copy of an object formed by rays of light.

Figure 2 shows how a plane mirror forms an image. To produce your image in a mirror, rays of light strike you and reflect. These reflected rays then strike the mirror and are reflected into your eyes. The dashed lines show how your brain interprets where the rays are coming from. The rays appear to come from behind the mirror. Your image appears the same distance behind the mirror as you are in front, and the image is right side up. If you walk toward the mirror, you'll see your image also move toward the mirror. A plane mirror always produces a virtual image. Although you can see a virtual image, this type of image cannot be projected onto any surface. A virtual image is a copy of an object formed at the location from which the light rays appear to come. It is important, however, to realize that the rays do not really come from behind the mirror.

Figure 2 The girl sees a virtual image of herself in the plane mirror. Virtual images such as this cannot be projected onto a screen. Note also how light rays from the object (the girl) reflect from the mirror's surface and obey the law of reflection. Interpreting Photos What do the dashed lines represent?