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Homework Help: Sound Intensity and Bird Watching

  1. Mar 24, 2012 #1
    1. The problem statement, all variables and given/known data
    A bird watcher is hoping to add a particular song bird to the list of species she has seen. If a person, only 2.35 m from the bird, hears the sound with an intensity of 1.9 10-6 W/m2, how far could the bird watcher be from the bird and still hear it? Assume no reflections or absorption of the bird's sound and that the faintest sound that can be heard has an intensity of 10-12 W/m2.

    2. Relevant equations
    I2/I1 = (r1/r2)^2
    I1 = 1.9e-6 W/m2
    I2 = 10e-12 W/m2
    r1 = 2.35 m
    r2 = ?

    3. The attempt at a solution
    I rearranged the equation to solve for r2
    I got r2 = √(I1 * r1^2/I2)
    I plugged in the numbers and got 1024.34 meters
    but the problem is saying that I did it wrong.
    Is there another formula or did I just mess up somewhere in solving this?
    Would appreciate help before Monday.
  2. jcsd
  3. Mar 24, 2012 #2

    See Intensity is inversely proportional to square of distance which is exactly what you used.

    So your equations are correct.

    Plug in the values again :-)
    Last edited: Mar 24, 2012
  4. Mar 25, 2012 #3
    Thanks for the reassurance. However, I found out that my value for the Intensity of the threshold of hearing was wrong by a power. Thanks though
  5. Mar 25, 2012 #4

    Yeah using 10^(-11) W/m^2 yields exactly the answer in your Post 1.
    Last edited: Mar 25, 2012
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