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Homework Help: Destructive Interference

  1. Oct 17, 2007 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations

    destructive interference occurs at 0.5(lambda), (3/2)(lambda),...

    3. The attempt at a solution

    I found the path difference to be:

    and this has to be equal to (n)(lambda)/2 where n is an odd integer for destructive interference

    this does not work out algebraically for me...as the x^2-x^2=0

    is this path difference not correct?

    do I just use f(n)=(nv)/(2d) to find d?
  2. jcsd
  3. Oct 17, 2007 #2
    Why did you do: x^2-x^2=0? Where does that come from?
  4. Oct 18, 2007 #3
    ok I found my path difference to be sqrt(4+x^2)-x

    so if I equate this to (n)(lambda)/2

    then: sqrt(4+x^2)-x=(n)(lambda)/2


    there is my problem...
  5. Oct 18, 2007 #4
    Do you know how to find lambda?
  6. Oct 18, 2007 #5
    Oh, (sqrt(4 + x^2) - x)^2 = (sqrt(4 + x^2) - x) * (sqrt(4 + x^2) - x)
    You don't just square the terms.
  7. Oct 18, 2007 #6
    ah yes...of course

    I think that should be the proper way to solve this problem...at least for a and b

    now on to c...
  8. Oct 21, 2007 #7
    ok I do not understand c
    can anybody help?
  9. Oct 21, 2007 #8
    I would say that the only way for which there be no destructive interference is if x is 0
    but that revelation is really vague for me...could it be correct?
  10. Oct 21, 2007 #9
    the I get f=86Hz
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