Dr. Gadget's Science Machine
The magic of gazing into a mirror

By Joe Lazslo

When you look into two mirrors, are you looking at your own reflection? Sometimes you are, but if the mirrors are arranged carefully, you may be looking at a reflection of your reflection instead. Illustration by Greg Taylor • The Honolulu Advertiser

Aloha! Did you stand in front of a mirror this morning? Have you wondered how a mirror works, or why you can see yourself?

Light from some source like light coming in the window has to hit you, bounce off and strike the mirror. Then it bounces off of the mirror and into your eyes. All of this bouncing around of light is known as reflection.

The picture you see of yourself is called an image.

Here are some concepts and experiments to try out.

• When you look in a flat mirror, do you see yourself as others see you? Try this: Wink your right eye. When you look in the mirror, which eye does your image wink back at you? The left one!

You do not see yourself as others do. Why? Because the light reflects back on the same side that it strikes the mirror.

• How can you work with your mirrors so that you see yourself as others see you?

Find two flat mirrors that are square or rectangular and about the same size, and a protractor. Carefully tape the mirrors together along one edge. Then stand them up and move them until the angle between the two mirrors is 90 degrees, or a right angle.

Look into them and wink your right eye. Which eye does your image wink? The right eye! Why? When you have the mirrors at 90 degrees, the light from the right side of you face strikes the right mirror, is reflected into the left mirror, and finally reflected back to you on the "other" side. Same for the light from the left side of your face.

• Stand in front of your bathroom mirror. Hold up a hand mirror facing the bathroom mirror, just under the level of your eyes. Move the hand mirror around until you see a series of repeating images. They get smaller and smaller until they disappear. This is like a tunnel to infinity.

Why do you see all of these images of yourself holding the mirror in front of you? Because the beams of light are continuing to bounce back and forth between the two parallel mirrors. Your viewing angle causes the reflected rays to reach a point where they are are no longer reflected to you. That's what you see as the "end" of the tunnel.

• Let's look at multiple images with the two flat mirrors you have taped together. With the mirrors still at 90 degrees, place a coin between them. How many images do you see? You should see three images, plus the coin.

Now try to figure out to what angle you need to move the two mirrors to get four images and the object, or a total of five? Try it. I saw four images at about 80 degrees.

Can you get five images and the object, or a total of six? What angle do you think you will need between the mirrors? Try it. I saw the five images at 60 degrees. (By the way, this is the same angle you would find between the three mirrors in a kaleidoscope.)

Notice all five images seem to be the same distance from the place where the two mirrors meet. These are multiple images which are a bit different from the repeating images in the tunnel to infinity. What causes the five images?

Try this: Draw and number the images 1 through 5 in a clockwise direction as you look at them.

The primary image, which is seen in Nos. 1 and 5 closest to you, are caused by the light from the coin striking the nearest mirror and being reflected. The secondary image, which is seen in Nos. 2 and 4, is caused by light from primary images 1 and 5 striking the opposite mirrors, and being reflected. The tertiary image, No. 3, is caused by the light of Nos. 2 and 4 striking the mirror and being reflected.

Images can act as objects and make new images when the mirrors are at angles to each other. This will happen as long the beams of light can reflect off of the mirrors as new images. What is the largest number of images you can get by changing the angles? Try it. Have fun with your mirrors. A hui hou!

"Dr. Gadget's Science Machine" is written by Joe Laszlo, a retired science teacher and winner of a Presidential Award for Excellence in science teaching. His column alternates in this spot with "Hawai'i Nature Squad."