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Homework Help: Amplitude and Pa

  1. May 4, 2009 #1
    Webassign night again!!
    1. The problem statement, all variables and given/known data
    During normal conversation, the amplitude of a pressure wave is 0.023 Pa.
    (a) If the area of the eardrum is 0.56 cm2, what is the force on the eardrum?

    (b) The mechanical advantage of the three bones in the middle ear is 1.5. If the force in part a is transmitted undiminished to the bones, what force do the bones exert on the oval window, the membrane to which the third bone is attached?

    (c) The area of the oval window is 0.026 cm2. What is the pressure increase transmitted to the liquid in the cochlea?

    2. Relevant equations
    I'd assume I'd be using dB=20log(P/P) But I'm not sure how to apply that to any of these equations.

    3. The attempt at a solution
    Can't even figure out where to start. I'm sure with some starting advice, or at least how to solve the first part I could figure it out.
  2. jcsd
  3. May 4, 2009 #2
    Maybe you could start with F = pressure * area
  4. May 4, 2009 #3
    well, to convert cm^2 to m^2 do I have to do anything special besides just dividing by 100?
  5. May 4, 2009 #4
    You have to do more than divide by 100. If it was converting cm --> m dividing by 100 would be ok.

    Think of it this way in terms of multiplication- You want to cancel the units until you have m^2.


    1cm^2 *(1m^2)/(100^2 cm^2) = .0001 m^2.

    So you know there are 100 cm in a meter. So if everything is squared, that must mean that there are 100^2 cm^2 in a m^2. So as you see above, when looking at the units, the cm^2's cancel out and you are left with m^2.
  6. May 5, 2009 #5
    Should'a been able to figure that out, but got it now. 100% on webassign, all right. Thanks for helpin me out guys.
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