Your eye contains a part called a lens. Like the lens of a camera, this eye-part focuses light. But unlike the glass lens of the camera, yours is made of living muscle. Like other types of muscle, it can stretch and contract. By changing its shape, the lens can focus distant or close-up objects onto the light-detecting part of the eye (called the retina; without the action of the lens, our visible world would be a blur.
Things Required:
White wall
Clear glass marble
Directions:
Stand next to a white wall. Make sure your body is well illuminated Hold out a clear glass marble several inches from the surface of the wall. Look closely at the wall just below the marble. What (or whom) do you see?
Now place the marble over a screw or scratch on the wall. Move the marble up and down until the screw is in focus. How does the marble affect the image of the screw?
This Is What Happens:
The marble acts like a lens. Light rays that are reflected off your body enter the marble. They exit the marble and are cast onto the wall. If the marble is placed at the correct distance, a finely focused (and very reduced) image of your body can be seen on the wall screen.
At the same time, your body shrinkage was occurring, the marble was magnifying wall objects. The screws and scratches appeared larger because the marble had spread out their reflected light rays.
