Ring of standing waves
Practical Activity for 14-16
Circular waves on a water surface can produce a standing wave pattern.
Apparatus and Materials
Using a trough or large bowl:
- Glass trough, large round
- Wooden block Using a Petri dish and vibrator-driven dipper:
- Signal generator
- Vibrator, with some form of dipper attached
- 4 mm leads, 2
Health & Safety and Technical Notes
Beware of water on the laboratory floor. Make sure you have a sponge and bucket handy to mop up spills immediately.
Using a trough or large bowl: A trough with diameter 30: 40 cm is adequate. Alternatively use any large plastic bowl.
The driving frequency needs to be high to get a number of wavelengths in the circumference.
It may be better to use a rapid rocking motion.
Using a petri dish and a vibrator-driven dipper: Put a little water in the Petri dish. The dish could be supported, with a screen about 0.1 m below it and a 12V lamp above it, making it a miniature ripple tank. The dipper will produce ring patterns of waves in the dish.
- Half fill the trough with water.
- Place the wooden block in the water surface near the edge. By moving it up and down, excite fairly high frequency ripples and establish a pattern of standing waves.
- This is a tricky experiment to do, and can result in water everywhere. An integral number of half-wavelengths need to fit into the circumference of the trough.
- You may find that a rapid rocking motion of the hand more effectively produces a standing waves pattern.
- This is similar to the experiment "Vibrations in a rubber sheet".
- You may wish to link this demonstration to the wave-mechanical model of the atom, with electron waves fitting into the atom.
This experiment was safety-tested in February 2006