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Code Number: 3B55.55
Demo Title: Diffraction Around an Obstacle - Through A Fan
Condition: Excellent
Principle: Diffraction of Sound
Area of Study: Oscillations & Acoustics
Equipment:
PVC Tube, Buzzer and Battery (Doppler App.), and Fan.
Procedure:
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.
References:
- 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.