• Wax blocks

• A sharp knife

• The ripple tank from the Ripple Tank experiment

• A pencil or dowel, or a six inch ruler, to create straight line waves

1. Cut a wedge shape from one end of each of two wax blocks.
2. Place the blocks in the tank to make a barrier with the wedged ends forming an opening of about one-quarter inch.
3. The barrier should be about four inches from the end of the tank where the pencil or ruler is.
4. Generate straight-line waves.
5. Watch the screen to see what happens to the waves as they go through the opening.
6. The waves emerge from the opening with a semicircular shape.
7. Change the size of the opening by moving the blocks closer and farther apart and see what effect this has on the emerging wave.

When the opening between the wax blocks is about the same size as or smaller than the wavelength, you can see how the wave diffracts through the opening.

Diffraction is the bending of a wave around an obstacle. The waves that emerge from the narrow opening are semicircular and very similar to the waves made by the eyedropper. As the opening between the wax blocks get larger, the diffraction of the wave becomes less obvious. In the next experiment you will use diffraction to create two circular wave sources to see interference.

To find this experiment and many more please read Light Action! Amazing Experiments with Optics by Vicki Cobb and Josh Cobb, illustrated by Theo Cobb. To purchase a copy click here.