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Homework Help: Soundwave Intensities and power

  1. Jan 29, 2012 #1
    1. The problem statement, all variables and given/known data

    1. Question : A point source emits 34.0 W of sound isotropically. A small microphone intercepts the sound in an area of 0.510 cm2, 185 m from the source. What is the sound intensity at that distance?
    What is the power intercepted by the distance?

    2. Relevant equations


    3. The attempt at a solution

    so far i have gotten the intensity as I=P/A,
    I=7.91*10^-5 W/m^2

    However for the second part of the question to calculate power, it is not correct. I use P=IA
    with the same area but it will not work properly:
    P=(7.91*10^-5W/m^2)(5.10*10^-3m2 + 4pi(185m)^2
    P=34.0 W (which is incorrect)

    Where is the flaw in this equation?
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jan 30, 2012 #2
    For the first part,

    I_atmic = P/A where P and R are given in the problem, and A = 4∏R^2

    For the second part P_atmic = [I_atmic]a = Pa/A where a is the area of the mic.
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