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Every kid dreams of a magic wand with which they can do anything they want. A dash of the wand, and presto, a goblin appears or disappears, a bar of chocolate enters the world from nowhere, or an image stays in the mind’s eye.

This last possibility becomes very real with this neat magic wand experiment.

• A slide projector
• A 35 mm slide
• A moveable screen or white poster board
• A pencil, wooden dowel or yardstick

1. Place the moveable screen or poster board approximately 6 feet in front of the projector. Next, place a slide into the projector, turning the projector on, and focusing it appropriately.
2. Now, remove the screen.
3. Hold the wand horizontally in the place where the screen was located. Now wave the wand quickly up and down. Can you see the picture appear as the wand moves?
4. Wave the wand around at an angle, or trace a cone or cylinder in the place where the screen stood. Does it create a strange image?

What Happened:

Once you remove the screen, the image has nowhere to appear. When you move the wand in front of the image, the wand reflects the light just as the screen would, and your eyes can pick up the picture.

When light reflects in your eyes, it creates an image on your eye’s retina. The eye holds onto this image for about 1/30th of a second. This is long enough for your eyes to piece the image together, forming a composite picture. This phenomenon is called “persistence of vision,” and it occurs when the rods and cones–which detect light in your eyes– continue to send electrical signals to your brain, even after a very brief appearance of light.