3B55.55 - Diffraction Around an Obstacle - Through A Fan

Code Number:
Demo Title:
Diffraction Around an Obstacle - Through A Fan
Diffraction of Sound
Area of Study:
PVC Tube, Buzzer and Battery (Doppler App.), and Fan.

Put the buzzer and battery assembly in the end of the tube and then point the other end of the tube either above or below a table. This will show some properties of the diffraction of sound around an object.

Hold the buzzer and battery assembly on the back side of a running fan while the class listens to the sound coming through the fan. Properties of the dependence of diffraction on wavelength may be explored with this demonstration.

  • Joe L. Ferguson, "Why Can We Hear but Not See Around a Corner?", AJP, Vol. 54, #7, July 1986, p. 661.
  • Bertram Schwarzschild, "Diffraction Around the Head Makes Hearers Mislocate Sound Sources", Physics Today, March 2010, p. 16.
  • Robert Ehrlich, "Q.4, Sound Through a Fan", Turning the World Inside Out, p. 195.
  • Robert Ehrlich, "Q.6, Moving a Beeper Below Desk Level", Turning the World Inside Out, p. 197.
  • Robert Ehrlich, "Q.5, Diffraction with a Rolled-Up Carpet", Turning the World Inside Out, p. 196.
  • Jearl Walker, "3.21, Cheerleader's Horn, Foghorns", The Flying Circus of Physics Ed. 2, p. 154.

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