Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds
 

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.

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


a Half fill the trough with water. 

b 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


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 This is similar to the experiment Vibrations in a rubber sheet.

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

 

Related experiments


Vibrations in a rubber sheet

Standing waves on a rubber cord

Standing waves with a variable wavelength

Stationary waves in an air column

Longitudinal standing waves in rods

Longitudinal standing waves

Vibrations on a loudspeaker cone

Musical instruments