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Homework Help: Sound Interference Problem

  1. Jan 31, 2008 #1
    1. The problem statement, all variables and given/known data
    Two in-phase loudspeakers are 2.55 m apart. They emit sound with a frequency of 370.0 Hz. A microphone is placed half-way between the speakers and then moved along the line joining the two speakers until the first point of constructive interference is found. At what distance from that midpoint is that first point? The speed of sound in air is 340 m/s

    2. Relevant equations
    λ = v/f

    3. The attempt at a solution
    Ok, so first thing is to find the wavelength, v/f = 340/370 = 0.919m
    What is wanted is constructive interference, so the path difference/λ should be a whole number, and the first point of constructive interference would be when path difference/λ = 1.
    Now the midpoint between the two speakers is 2.55/2 = 1.275m.
    Not really sure how to put it all together.
  2. jcsd
  3. Jan 31, 2008 #2
    Since you're solving for the distance between the central maximum and the first order maximum, [tex]L = \lambda[/tex].
  4. Jan 31, 2008 #3
    1.275-0.919=0.356 will be distance from midpoint to point in which became interference.
  5. Jan 31, 2008 #4
    No, the first constructive interference will occur 0.919 m from the midpoint.
  6. Jan 31, 2008 #5
    I've actually tried both those answers and they didnt work.
    I tried 2.55-0.919 = 1.63 then subtracted the midpoint, 1.275 from it, = 0.356m
  7. Feb 2, 2008 #6
    The question is asking for the distance from the midpoint. Your final answer would be 0.919 m.
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