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

Vibrations of circular wire rings

Demonstration

This simple experiment shows standing waves on a wire ring.

Apparatus and materials

  • signal generator
  • vibrator
  • xenon stroboscope
  • copper wire, 0.90 mm diameter, or thinner steel wire
  • 4 mm leads

Health & Safety and Technical notes


Read our standard health & safety guidance

wire ring

Form a length of wire (about 1 m) into a circle and. attach it to a vibrator so that it stands vertically. One method is to form the two ends of the wire into loops and anchor them between washers on the vibrator shaft.

Copper wire, 20 s.w.g., is satisfactory but the large amplitude standing waves at lower frequencies tend to deform the ring. Thinner steel wire works better. A 10 mm strip of 10.05 mm thick steel works very well with a circle of about 0.1m diameter.

Safety note: Using the xenon stroboscope, teachers should be aware that frequencies around 7 Hz have been known to cause epileptic fits in certain people. Ask your students if any know that they are susceptible to this response.

Procedure


a Vary the frequency of the input signal to find the resonance modes of vibration.

b Questions to consider: How are the resonance frequencies related to each other? To the number of nodes on the loop?

Teaching notes


1 To get standing waves on the wire loop, it must be vibrated at specific frequencies. In the figure below, (a) shows the fundamental mode of oscillation and (b) shows the 3rd harmonic.

Harmonics in the wire ring

2 Alternatively, this simple experiment could be used as one station in a circus of class experiments on standing waves and resonance.

3 The standing waves should be viewed stroboscopically, as well as by eye, to give students a clear understanding of their nature.

This experiment has yet to undergo a health and safety check.

 

Relating experiment


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 in a rubber sheet
Vibrations on a loudspeaker cone
Ring of standing waves
Musical instruments

 

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