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Homework Help: Sound waves interference

  1. Mar 20, 2005 #1
    Here is a problem i do not know how to set up:

    Two speakers, driven by the same oscillator (f=200Hz). They are located on a vertical pole 4m from each other. A man walks straight toward the lower speaker, perpendicular to the pole. How many times will he hear a minimum in sound intensity and how far away from the pole is he at these moments? (take speed of sound to be 330m/s).

    Any help is appreciated especially equations to use and how to start this.
     
  2. jcsd
  3. Mar 20, 2005 #2
    Very nice problem thenewbosco. You must begin with the equations of the oscillations received by the observer:

    [tex] y_1=A sin(\omega t-kx)[/tex]
    [tex] y_1=A sin(\omega t-k \sqrt(x^2+h^2))[/tex]

    (x is the distance from the pole to the observer and h the pole's height and [tex]k=\frac{2 \pi}{\lambda}[/tex])

    In a first approximation (observer far away from the sources) we'll simply add these oscillations:

    [tex]y=y_1+y_2=...=2Acos\frac{2 \pi}{\lambda}(x-\sqrt(x^2+h^2))\cdot sin(\omega t+.......)[/tex]

    The amplitude of the resultant oscillation is given by the first part :
    [tex]2Acos(.....)[/tex]
    and we must find x that gives you cos(....)=0 (interf. min.)
     
    Last edited: Mar 20, 2005
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