Physlet Illustration: Wave Interference

 

 

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A microphone lies along the line between two loudspeakers. The speakers are connected to the same source of sound, which has a frequency of 85 Hz. The display grid is in meters. The graph shows the sound waves arriving at the microphone, as a functions of time, from each speaker, and also shows the sum of the two waves. Move the microphone back and forth to study the changing interference of the two sound waves. Can you find the locations of constructive and destructive interference?

Hints:

  1. For what microphone position(s) do the wave crests from the two speakers arrive at the same time? What does their sum look like? What would this sound like?
  2. For what microphone position(s) do the waves from the two speakers arrive such that a crest from one meets a trough from the other? What does their sum look like? What would this sound like?
  3. From your investigations, can you determine the wavelength of the sound? (Remember that it is the difference between the two sound paths that determines the interference.) 

Reference

See Walker, Section 14-7

Illustration written by Steve Mellema