Ring of standing waves

Demonstration

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.

Read our standard health & safety guidance

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.

Procedure

1. Half fill the trough with water.
2. 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.

Teaching Notes

• 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