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Homework Help: Find the point of destructive interference of two waves.

  1. Aug 3, 2012 #1
    1. The problem statement, all variables and given/known data

    Two coherent in-phase point sources of sound are located at the points (-2 m, 0 m) and (2 m, 0 m). If the wavelength of the sound is 0.9 m, at which of the following x values on the x-axis does destructive interference occur?

    2. Relevant equations

    Wave Equation:
    y(x, t) = Acos(kx + ωt)

    3. The attempt at a solution

    I have no idea how to even start this one. Could someone just nudge me in the right direction? This is the last practice problem I have to do, but I am really stuck.
  2. jcsd
  3. Aug 3, 2012 #2


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    Well, maybe start with this: what is the condition for destructive interference to occur?
  4. Aug 3, 2012 #3
    Well, let's see. They have to be out of phase by 180 degrees. But the part that confuses me is that the problem says they have the same phase.
  5. Aug 4, 2012 #4


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    The sources are in phase.

    However, the waves move and that's at a finite speed.
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