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Oscillation / Soundwaves Question - Phase difference?

  1. Feb 16, 2013 #1
    An observer stands 3 m from speaker A and 4 m from speaker B. Both speakers,
    oscillating in phase, produce 170 Hz waves. The speed of sound in air is 340 m/s.
    What is the phase difference (in radians) between the waves from A and B at the
    observer’s location, point P?


    And I have no idea how to solve this :confused: :uhh:

    Basically looks like:

    P---------B (4m away)
    |
    |
    |
    |
    A (3m away)
     
  2. jcsd
  3. Feb 16, 2013 #2

    tms

    User Avatar

    Think about what what a phase difference means, and then think about wavelengths and distances, and how all three are related.
     
  4. Feb 16, 2013 #3
    I get that graphically a phase shift means it's literally shifted across the x-axis. But I can't think of an equation that would relate this an the distance.
     
  5. Feb 16, 2013 #4

    tms

    User Avatar

    If you draw two sine waves, one shifted a bit relative to the other, on the same graph, a distance should jump out at you.
     
  6. Feb 16, 2013 #5
    :confused: But we don't know the phase...

    I get that they're 1m apart and it covers 340 m every second so the phase would be out of sync by 1/340.. do I convert that to radians then?
     
  7. Feb 16, 2013 #6

    tms

    User Avatar

    The 340 m/sec is the speed of sound. You need to know the wavelength of the emitted sound, and compare that to the distance between the speakers.
     
  8. Feb 16, 2013 #7
    Okay, so it travels 170 waves / s and one of the speakers is 1m further so it's out of phase by 170 waves (not sure how to get that into rads) but I feel like we need the speed of sound in there somewhere..
     
  9. Feb 16, 2013 #8

    tms

    User Avatar

    You are assuming that the wavelength is one meter; that is something you need to calculate using the wave speed and the frequency.
     
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