Standing Wave
Light, Sound and Waves

Longitudinal standing waves in rods

Practical Activity for 14-16 PRACTICAL PHYISCS

Demonstration

With this experiment you can show standing waves, either transverse or longitudinal, in a rod or rods.

Apparatus and Materials

  • Glass, steel, or brass rod, about 10 mm diameter and about 1.5 m long
  • G-clamp
  • Wooden blocks
  • Cloth
  • Rosin (for metals)
  • Alcohol (for glass)

Health & Safety and Technical Notes

Read our standard health & safety guidance


Procedure

  1. Hold the rod fairly firmly with rosined fingers, or a dampened cloth, and stroke it. What is the wavelength of the standing wave being produced?
  2. If you can find a way of estimating the frequency of the sound emitted, then go on to estimate the speed of sound in the rod.

Teaching Notes

  • In its fundamental mode of oscillation, the rod will have a node at the fixed end and an antinode at its free end. Thus the wavelength will be twice the length of the rod. The standing wave is audible as a sound of pure frequency.
  • By displacing the free end slightly and then releasing it, you might also show an equivalent transverse wave, which is visible.
  • Alternatively, the experiment could be used as one station in a circus of class experiments.
  • A more dramatic version of this demonstration, often called the ‘singing rod’, uses an aluminium rod as much as 2 m in length. See, for example, this video:

    Watch video


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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