Water-Drop Lens: Can You Make a Magnifier out of a Water Drop?

Problem

Can you make a magnifier out of a water drop?

Materials

• flat toothpick
• petroleum jelly
• sheet of newspaper
• eyedropper
• tap water

Procedure

1. Use the end of the toothpick to smear a thin layer of petroleum jelly over a word on the newspaper.



2. Fill the eyedropper with water, and squeeze one drop of water over one of the printed letters that have been covered with jelly.
3. Describe the shape of the water drop.
4. Look through the drop of water at the letter beneath it. Compare the size of the letter viewed through the water drop with the letters not covered by the drop.

Results

The water forms a round drop on top of the oily paper. The bottom of the water drop is flat, but the top is curved. The letter under the water drop looks larger than the letters not underwater.

Why?

The paper under the water drop was covered with petroleum jelly to keep the water from soaking into the paper. Water and oil do not mix; thus, the water forms a dome on top of the oily surface. The rounded surface of the water drop acts like a single convex lens (a lens that is thicker in the center than on the ends; it curves outward on one side and is flat on the opposite side). A magnifying lens is made with a double convex lens (a lens thicker in the center than on the ends; it curves outward on both sides).

Let's Explore

1. Does the size of the drop affect its magnification? Repeat the original experiment using the toothpick to place smaller drops of water on the paper. Repeat again, using the eyedropper to add several drops to the same place on the paper, thereby forming one big drop. Science Fair Hint: Make diagrams to represent the size of the image viewed through the water drop. Next to the drawing, place the actual letter being viewed. Use these diagrams as part of a science project display.
2. Would the purity of the water affect the magnification of the drop? Repeat the original experiment using different samples of water, such as distilled water, bottled spring water, and tap water from different sources.

Show Time!

1.  
   1. Make a hand-held magnifying lens by rolling a piece of clay into a long, thin rope. Use the clay to form a small circle in the center of a sheet of transparent plastic. Fill the center of the clay circle with water. Hold the plastic sheet over a sheet of newspaper and look through the water. Raise and lower the plastic sheet to get the best image.
   2. Change the size of the clay circle and repeat the previous experiment. For each size circle, ask a helper to measure the distance from the lens to the newsprint that gives the best image. Photographs of the experiment with the distances labeled can be displayed.

Check It Out!

Light coming from an object is bent as it passes through a lens. Find out more about the bending or refraction of light rays. Where is the focal point of a lens? What is the focal distance?

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Janice VanCleave's Microscopes and Magnifying Lenses
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