Introduction: 3 Dimentional Display

SUBJECT: Light and Optics

TOPIC: Reflection

AIM: To see images of images of images can repeat forever.


2 plane mirrors

Some kind of stand


Here you see two mirrors that face each other, such as in a barber shop or a beauty salon, that produces seemingly endless line of images fading into the distance.


Cut two holes about 1 inch (2.5 cm) in diameter near the center of one of the mirrors. You can get the effect without the hole, but the hole gives a more interesting perspective. You can even create the hole on a glass mirror tile by scraping away the silver backing. Stand the mirrors so that their reflecting surfaces face each other and are

parallel to each other. The mirrors can be anywhere from a few inches to a foot apart. You can make a wooden stand for each mirror by cutting a slit along the length of the flat side of a piece of 1 x 4 inch (2.5 x 10 cm) pine. Then slip the mirror into the slit. With the reflecting surfaces facing each other, look through the hole into the space between the mirrors. (If you didn't bother making a hole, just look over the top of one mirror.) You can also try placing either your finger or some other object between the mirrors. If you place an object between the mirrors, notice that there is a repetitious pattern in the orientation and spacing of the images. Objects with contrasting colors on the front and back (such as red and white) show this well. Successive images alternate from front view to back view. If the original object is closer to one mirror than to the other, the distance between successive images will alternate from close together to far apart - making the images seem to be grouped in pairs, with a front side always facing a front side, or a back side always facing a back side.


In this light-ray diagram, the solid lines show the actual path of the light rays; the dashed lines show the path of the light rays projected by your brain. You see images where the dashed lines come together. This light-ray diagram shows the rays that come from the front of an object and those that come from the back. After the first reflection, you see one image in each mirror where the dashed lines come together (1). After the second reflection, you see a second image in each mirror (2), and so on. As you look at the images formed in one of the mirrors on the diagram, notice that there is an alternation of front and back views, that the images appear to be grouped in pairs, and that a front side is always facing a front side and a back side is always facing a back side. This corresponds to what you actually observe in the mirrors.


Two parallel mirrors produce seemingly endless line of images fading into the distance.