Thomas Peter Brennan
UBC Department of Physics and Astronomy, 2012
This website is adapted from a demonstration for young physicists to show fundamental characteristics of waves. I used a table of water to show several properties of wave mechanics. This site is meant to describe the demonstration, and preserve the presentation for future instruction.
A PowerPoint presentation, adapted for the web from the original.
Videos of the demonstrations
About the demonstration
Waves are one of the most commonly experienced physical phenomena. Indeed, much of the human experience comes from waves, from the light that allows us to see, to the sounds we hear, to the electrical signals within our brains and nervous systems.
But instruction in wave theory can tend to be quite abstract: waves are drawn on whiteboards, and students are told about their properties, some of which can be counterintuitive. There are a host of excellent visual demonstrations of wave behaviour, including Java applets (some of which can be found on PhET). But I wanted to devise a physical demonstration that was able to show these behaviours, to aid students in learning about waves. It is one thing to see something on a screen, but it is another to see it with one’s own eyes.
Supposing that perhaps the most ubiquitous experience of wave mechanics is in water, I determined to use water to demonstrate. I had a plexiglass table built, with a lip to hold about half an inch of water. When a bright light is shone down on the water, through the table, the shadows of any ripples or disturbances in the water are projected onto the ground. This allows for a variety of demonstrations.
As constructed, this demonstration was best for a small group, of no more than 10 students who could surround the wave table. However, it can be adapted for classrooms by use of live projection equipment—even a basic web-cam on a computer connected to a projector enables larger groups to experience the demonstrations.
The possibilities for wave demonstrations with this apparatus are quite wide. In my presentation, I focused on the following:
Wave basics—wavelengths, amplitudes, frequencies, velocity
Interference—constructive and destructive
Single and double slit experiments, demonstrating diffraction