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Homework Help: Need help w/ problem: Sound intensity and energy

  1. Jun 21, 2009 #1
    1. The problem statement, all variables and given/known data
    A fan at a rock concert is 30 from the edge of the stage. The sound intensity level at the edge of the stage is 110 dB. The fan's eardrums have a diameter of 8.4 . How much energy is transferred to each eardrum in one second? (Hint: It may help to asume that the speaker is on the stage located 1.0 m from the edge.) Answer should be expressed in Joules.
    2. Relevant equations
    I=P/4πr^2, β=(10dB)log(I/Iinitial)
    3. The attempt at a solution

    Thanks for your help!
  2. jcsd
  3. Jun 24, 2009 #2


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    Homework Helper

    Why did you leave the distance units out when telling us the distance from the stage and the diameter of the eardrums?

    Anyhow, at 1 m from the speaker, sound intensity is 110 dB. What's the intensity 31 m away? (Hint: inverse square law.) Express that in watts per unit area, then multiply that by the eardrum's area, and you'll get the answer.
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