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Points of destructive interference of sound waves?

  1. Feb 14, 2015 #1
    1. The problem statement, all variables and given/known data
    Two speakers (S1,S2), emitting sound waves of frequency 340Hz and separated by a distance of 3 m, are driven by the same oscillator. A listener starts walking from point A to S2 Along the line that joins A and S2> How many points of destructive interference will be observe? Speed of sound in are is 340 m/s

    2. Relevant equations
    w=v/f

    3. The attempt at a solution
    Although, it seems quite easy,I've tried to solve it many times with no reasonable result,
    Wavelength will be 1 meter. And I don't know how to do after that.

    the right answer is 4 but how it comes?? Untitled.png Untitled.png
     
  2. jcsd
  3. Feb 14, 2015 #2

    mfb

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    What is the condition for destructive interference?
    This condition has one parameter that will vary as you go towards S1. What is its initial and final value?
     
  4. Feb 14, 2015 #3

    The condition says :
    for a destructive interference, (delta L/wavelength)=n.0.5
    But how can I apply it here?

    The initial value of delta L equals to 1 and the final value equals 1.
     
  5. Feb 14, 2015 #4

    mfb

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    I agree with the initial value, but not with the final one. What are the two distances to the speakers at the final position?
     
  6. Feb 14, 2015 #5
    Sorry, I meant 3
    The vertical distance between the two sources.
     
  7. Feb 14, 2015 #6

    mfb

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    Right, that allows to find how many times you get destructive interference. But the answer is not 4.
     
  8. Feb 14, 2015 #7
    I think that it is 3
    Am I right??
     
  9. Feb 14, 2015 #8

    mfb

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    Why 3?
     
  10. Feb 15, 2015 #9
    Oh , sorry
    delta L will be (3-1) =2
    So the numer is two.
    I think I'm right now .
     
  11. Feb 15, 2015 #10

    mfb

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    Looks right.
     
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