A drop of water as a lens

Curved mirrors change what you see in them. What about clear things with curved surfaces? Through a flat window everything looks its normal size. Would it, through a curved one?

Make a lens from a water drop (Activity 10.8). You need a flat strip of clear plastic or glass (a clear ruler works), a few drops of oil, a dropper, water, and some printed text.

Rub a few drops of oil on the strip to leave a very thin coating (wax works too). The oil stops the water spreading out flat, so it stays a nice round drop. Put a small drop of water on the oiled spot and look at it from the side: its surface curves outwards.

Now slide the printed page under the strip so a word sits right under the drop, and look down through it. The letters under the drop look bigger than the ones beside them.

The curved surface of the drop changed how the letters look: the drop is acting as a simple lens. A magnifying glass is a lens too, which helps you read small print by making it look bigger.

A lens is a piece of clear material, usually glass or plastic, with curved surfaces. Like mirrors, lenses can be convex or concave:

One big difference from mirrors: mirrors bounce light back, but lenses let light pass through. So you look through a lens, not into it.