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Homework Help: Sound wave interference destructive interference problem?

  1. Aug 28, 2012 #1
    1. The problem statement, all variables and given/known data

    Two identical loud speakers placed at A and B 2m apart produce sound waves of frequency 440 HZ and with a velocity 320 m/sec a small microphone was used and placed at C along a perpendicular line from AB if there will be a destructive interference at C find the length of BC, please break the answer down for me and explain it in details,

    2. Relevant equations
    i guess v=f x wave length
    path difference (m+0.5)wavelength

    3. The attempt at a solution
    I'll start by getting the wave length = velocity/frequency = 320/440= 8/11 but then what ? i don't see any way that could led me to length of BC
    Last edited by a moderator: Aug 28, 2012
  2. jcsd
  3. Aug 28, 2012 #2


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    Destructive interference occurs where a peak from one speaker meets a trough from the other. So perhaps draw circles of appropriate radius centered on a and b?
  4. Aug 31, 2012 #3
    i don't understand how can a wave coming from speaker A interfere with wave coming from B at C ! maybe draw a line from A to C and make some sort of triangle, but i don't see where this may get me ?
  5. Sep 1, 2012 #4


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    Yes, draw a line from A to C. And, also draw a line from B to C.

    If there is destructive interference, there is something you can say about the lengths of those two line segments.

    p.s. Welcome to Physics Forums :smile:
  6. Sep 2, 2012 #5
    Hey, ! Thanks, and i finally got the answer when i was in the physics class, and our teacher was like who got this ? and some guy raised his hand and told him the answer and how there are infinite answers because C could be anywhere, and I'm really sad that i got really shy and didn't have the nerve to say in a loud voice the answer and our teacher kept on praising this guy and telling him how smart he is and i got REALLY SUPER jealous, but it's not that hard anyway eh ?.
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