Standing Wave
Light, Sound and Waves

Vibrations of a loudspeaker cone

Practical Activity for 14-16 PRACTICAL PHYISCS

Demonstration

This experiment shows how AC oscillations from the generator become sound oscillations at the loudspeaker.

Apparatus and Materials

  • Signal generator
  • Large loudspeaker
  • Xenon stroboscope
  • 4 mm leads
  • Semolina or rice, a small amount

Health & Safety and Technical Notes

Read our standard health & safety guidance

Clamp the loudspeaker so that it faces upwards. Connect the low impedance output of the signal generator to the loudspeaker. Place a few grains of semolina or rice in the cone so that resonances show up clearly, as the generator frequency changes.

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

  1. Increase the frequency slowly from about 10 Hz to a few 100 Hz.
  2. Watch the resonance of a loudspeaker cone under stroboscopic illumination.

Teaching Notes

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.

Standing Wave
is a special case of Interference
is used in analyses relating to Resonating Pipe Oscillating String
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