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Sound Waves: Energy per second

  1. Feb 11, 2015 #1
    1. The problem statement, all variables and given/known data
    Standing 20m away from a tower generating 2500W of power how much energy/s hits each of your eardrums?
    Surface area of eardrum=55mm^2
    Assume that the speaker generates sound uniformly in a forward hemisphere.

    2. Relevant equations
    I=P/(4πr^2)
    r=20m
    P=2500W


    3. The attempt at a solution
    I=2500/(4π*20^2)=0.497W/m^2
    Surface area of eardrum=55mm^2=55*10^-6m^2
    0.497W/m^2*(55*10^-6)m^2=2.7*10^-5W
    The actual answer is 5.5*10^-5W, not sure what went wrong.
     
  2. jcsd
  3. Feb 11, 2015 #2

    TSny

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    Note that the sound spreads over a hemisphere (not a sphere).
     
  4. Feb 11, 2015 #3
    Oh that's sneaky, I'll have to pay more attention to that stuff in the future.
     
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