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Homework Help: Sound intensity, given frequencies

  1. Jul 14, 2012 #1
    1. The problem statement, all variables and given/known data

    The intensity of a sound wave at a fixed dis-
    tance from a speaker vibrating at 1.31 kHz is
    0.894 W/m^2.
    Determine the intensity if the frequency is
    increased to 2.33 kHz while a constant dis-
    placement amplitude is maintained.
    Answer in units of W/m^2

    2. Relevant equations

    I=(P/4pi*r^a) and L = 10log(I0/I1)

    3. The attempt at a solution

    I tried a proportion with frequency over intensity to where I did (1.31)/(.894) = (2.33)/(x) and got 1.59 but the internet program said it was wrong (I have 6 more tries). I then looked at my equation relating intensity to power and area which is the first equation listed above which is one of the many equations that we have learned in class. It seems like the most ideal equation but the problem is that I'm not given power and I don't know how to relate power to frequency. My guess is that maybe you solve for some sort of radius with the first part of the problem and then use that radius in the second part since it says that the displacement doesn't change. Thanks.
  2. jcsd
  3. Jul 14, 2012 #2


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    Roughly: Intensity [itex] \propto [/itex] Energy [itex]\propto[/itex] velocity squared [itex]\propto[/itex] frequency squared
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