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Homework Help: Find Pressure amplitude from given decibels

  1. Nov 18, 2011 #1
    1. The problem statement, all variables and given/known data
    A sound wave has an intensity level of 49 dB. What is the pressure amplitude of this wave?

    Po= 2x10^-5
    2. Relevant equations

    β=10log(I/I0)
    I≈P^2

    3. The attempt at a solution
    I can't figure out why I'm getting this problem wrong. So I set it up, 49=10log(I/I0)
    -> 4.9=log(I/I0) -> 10^4.9=(I/I0) From there, I replaced the intensity for pressure amp (equation 2) -> p=(2*10^-5)√(10^4.9)
    Pamp=.0056Pa

    ??
     
  2. jcsd
  3. Nov 18, 2011 #2

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    Hi Angie_Agnes! :smile:

    You calculation looks good.
    Any reason to doubt your result?
     
  4. Nov 19, 2011 #3
    yes, it's online homework and says it's wrong :(
     
  5. Nov 19, 2011 #4

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    Well, I think you have to tweak your result a bit then.
    I believe it is numerically correct, but these online homework sites can be a bit difficult with the exact phrasing.
    Btw, I'm assuming you did not make a typo in the problem statement...
     
  6. Nov 19, 2011 #5
    I copied and pasted the question, so no typo.... I typed it in as .005 Pa and .006Pa and both came up wrong. Frustrating!
     
  7. Nov 19, 2011 #6

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    With 2 significant digits in 49 dB, it should be 0.0056 Pa or 5.6 mPa.
    I can't make anything else from it.
     
  8. Nov 19, 2011 #7
    THANK YOU! got it right as .0056Pa. Awesome!
     
  9. Nov 19, 2011 #8

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    Huh? But that is your original answer from your opening post! :confused:
     
  10. Nov 19, 2011 #9
    I looked back at my past answers, I had entered it .005 and .006 at first, before entering it finally as .0056.
     
  11. Nov 19, 2011 #10

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    All is well that ends well! :wink:
     
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