Ring of standing waves
Circular waves on a water surface can produce a standing wave pattern.
Apparatus and materials
Glass trough, large round
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.
A trough with diameter 30 - 40 cm is adequate.
The frequency needs to be high to get a number of wavelengths in the circumference. It may be better to use a rapid rocking motion.
a Half fill the trough with water.
b Lay your hand 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.
1 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.
2 You can do a similar demonstration of standing waves in a loop of wire. Connect both ends of a length of wire (about 25 cm) to a vibrator, so that the wire is shaped into a circle. Drive the vibrator with a signal generator, to produce standing waves at various resonant frequencies.
3 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-checked in February 2006