Science Activity: Bend Light With a Lens

lens-like the one in a magnifying glass or one from a disposable camera
room that you can make very dark
light source-like a TV set or a brightly lit window
sheet of white paper

Look through your lens at these words or at your fingertip. Do things look bigger through your lens? If they do, your lens is a magnifying lens. It will work for this experiment.

Go into a room that has just one source of light. On a sunny day, a window works just fine. (Turn off any electric lights in the room.) At night, you can turn on your TV set and use it as a light source.

You're going to use your lens to make a picture of the light source. So you want a light source that will make an interesting picture. A picture of an ordinary lightbulb is just a round spot, which is pretty boring.

Important Warning!

Stand a few feet away from your light source. Hold your lens up so that light can shine through it. Hold the piece of paper on the other side of the lens so that light shines through the lens and onto the paper.

The paper is your screen-like the screen in a movie theater. The paper screen will reflect a picture made of light so that you can see it.

Start with the lens up close to the paper, and slowly move it away from the paper and toward the light source. Watch the pattern of light on the paper. When the lens is the right distance from the paper, you'll see a picture of the light source. The picture will be upside down and backward.

If you don't see a picture right away, keep trying. Try standing closer to the light source. Or try moving the lens farther from the paper. It may take some experimenting, but sooner or later you'll get a picture.

When you use your lens to make a picture of something that's brightly lit, you are doing the same thing that a movie projector does. In a movie projector, a light shines through a transparent picture, then through a lens. The lens takes the light from the picture and makes a big picture on the movie screen.

Warning

You may already know that you can use a lens to focus sunlight into a very bright circle. That circle can be hot enough to start a fire. For many kids, playing with a lens outdoors can be like playing with matches. Take appropriate precautions.

If you take a lens outside and use it to focus a circle of sunlight, DON'T stare at the bright spot. That spot of light is an image of the sun. You can hurt your eyes by staring at it, just as you can hurt your eyes by staring at the sun.


This and dozens of other cool activities are included in the Exploratorium's Science Explorer books, available for purchase from our online store .
	Published by Owl Books, Henry Holt & Company, New York, 1996 & 1997 ISBN 0-B050-4536 & ISBN 0-8050-4537-6 , $12.95 each

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