Physics Dept. Demonstration Manual

DVW18.1 - Interference Tubes Method II


To show that two sound waves of the same frequency cancel out if one has to travel 1/2 wavelength further than the other.

  • Custom PVC interference tube loop
  • Stand, 3-fingered clamp
  • Function generator, Wavetek
  • Speaker (University Sound model 1D30C-8)
  • Banana leads, two
  • BNC/Banana adapter


Set the frequency generator to generate a 2.1 KHz sine wave. Fine tune the frequency control to attain maximum sound output, with the top loop retracted. The sound is split into two paths which re-combine at the output. If the top loop is lengthened by 1/2 wavelength, the two sound waves interfere and very little output is heard.


The effect can be demonstrated to an entire class at once.


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