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Homework Help: Pressure Amplitude

  1. Dec 11, 2007 #1
    1. The problem statement, all variables and given/known data

    (a) What is the pressure amplitude of a sound wave with an intensity level of 124.5 dB in air?

    _____ N/m2
    (b) What force does this exert on an eardrum of area 0.520 10-4 m2?

    _____ mN



    3. The attempt at a solution


    if P is amplitude of pressure, then sound intensity (I) is proportional to P^2
    I/Io = (P/Po)^2
    dB = sound intensity level = 10 log[I/Io]
    124.5 = 10 log[I/Io] = 10 log[P/Po]^2 = 20 log(P/Po)
    log(P/Po) = 124.5/20 = 6.225
    P = Po [10]^6.225
    Po = reference pressure amplitude for human ear = 2*10^-5 N/m^2
    P = 2*10^-5*[10]^6.225
    P = 33.576 N/m^2
    ----------------
    Force on eardrum = P * area = 33.576*0.52*10^4 N
    F = 1.746 milli N




    This is what I did. But it is not giving me the correct answer...can anyone help me?
     
  2. jcsd
  3. Dec 11, 2007 #2

    dlgoff

    User Avatar
    Science Advisor
    Gold Member

    The given eardrum area is 0.520*10^-4? But in your force equation (Force on eardrum = P * area = 33.576*0.52*10^4 N) you have it as 0.52*10^4.
     
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