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Homework Help: Power from sound

  1. Aug 16, 2015 #1
    1. The problem statement, all variables and given/known data
    Fans at a stadium produce sound that is heard 1km away, the intensity level is 60 dB. How much acoustic power is generated by the fans?

    2. Relevant equations
    B = 10 log (I÷I_0)
    P=I*A

    3. The attempt at a solution
    I= 10^-12*6^10= 10^-6W/m^2
    P= 10^-6*4pi*1000^2 =12.56W

    However the right answer should be 6.28W
     
  2. jcsd
  3. Aug 16, 2015 #2

    NascentOxygen

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    Staff: Mentor

    Hi triforce. :welcome:

    Do you need to consider: would sound be absorbed, or reflected, by the stadium floor?

    There's a typo in your working, too.
     
  4. Aug 16, 2015 #3

    tech99

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    Gold Member

    As the sound is radiated into a hemisphere rather than a sphere, the surface area is halved.
     
  5. Aug 16, 2015 #4
    Ah! That makes sense!

    Thank you very much!
     
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