Water lens magnifying glass
Here's a great activity for teaching kids some basic optics.
You can make a simple lens (plano convex - which means flat on one side and curved on the other) with nothing more than a drop of water on top of some clear cellophane or plastic (you can usually find something suitable in old packaging material). Put the plastic over a newspaper then drop some water on with your finger. Experiment with drops of different shapes and sizes. If the plastic you've used is fairly rigid, try lifting it (slowly and carefully, so you don't disturb your water drop) and holding it at different distances from the paper. What difference does it make?
This is from our article on lenses.
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