How Many Images Can You Make with Mirrors?

Talk It Over

Why do you see a reflection in a mirror? Is it possible to see more than one? How many might you make?

Get

• 2 4" x 5" plastic mirrors* (3 for "Go Far")
• Plastic packing tape
• Protractor
• Ruler
• Pen
• Graph paper, 6 pieces
• Modeling clay
• Coin
• Camera or drawing materials

Go

1. Stand the mirrors vertically and tape them together along their long edges so they are hinged, like this:
2. Move your hinge back and forth a few times. It should hold, but still allow the mirrors to move freely in all directions.
3. On separate pieces of graph paper, use your protractor to mark angles of 30°, 36°, 45°, 60°, 90°, and 180°. If you don't know how to do this, get an adult to help you.
4. On each piece of graph paper, find a spot in the center, between the two angle lines, and 8 cm (about 3 inches) out from the point of the angle. Mark that spot.
5. Test your angles one at a time. Put the modeling clay at the center point you marked. Set the coin upright in the clay. Position your hinged mirrors on the angle lines you drew, like this:
6. Take a photograph or make a drawing to record what you see. Also record the number of coin images in a data table.

Stay Safe

Don't use glass mirrors. Their edges can be sharp.

Go Easy

Try only the 180°, 90°, and 60° angles.

Go Far

This experiment works because light bounces off mirrors at predictable angles. If the bounced light hits another mirror, it bounces again, also at a predictable angle. It can do this several times before it reaches your eye, depending on the angle between the mirrors. A mathematic rule predicts how many images are visible. See whether you can discover it.

Expand your experiment by setting your hinged mirrors on a third mirror. See how many images you can count at the triple intersection.

Plastic mirrors are available in many shapes and sizes, including convex, concave, and dome. Design experiments that will let you assess the numbers and forms of the images you obtain with them.

Show Your Results

Record the number of images you see in a table like this for "Go Easy":

Make a bar graph that shows the number of images (on the vertical axis) by the angles you tried (on the horizontal axis).

For "Go," add smaller angles to your data table and your bar graph. State the mathematical rule that relates angle to the number of images. For "Go Far," design data tables and graphs to match the experiments you conduct.

For all projects, display your photographs or drawings along with any conclusions you drew from your data. Display your materials along with your project so others can try some experiments for themselves.

Tips and Tricks

• When counting images, your total is the real coin plus the images you see in both mirrors.
• Turn the coin so that heads faces one mirror and tails faces the other. Then look at the images. What do you notice about them? Report this observation as part of your project.

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CliffsNotes Parent's Crash Course Elementary School Science Fair Projects
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