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Homework Help: Thin films interference

  1. Aug 16, 2007 #1
    After I read many articles about measuring film thickness by interference method.

    I tried to calculate flow that papers but I can't

    the equation is

    d= (y1*y2)/(2*(n1y2-n2y1))

    for an easy I approximate n1 =n2


    d= (y1*y2)/(2*n(y2-y1))

    y1 = 350 nm
    y2 = 380 nm
    n = 2.35

    I want to find out "d"

    it seems to be easy

    but I always get d = 944 nm

    unfortunately, it's wrong

    d have to be 472

    that means I forgot to divide 2 in this eq.

    however, the eq use to be right.

    I don't know what's wrong in my calculation.
  2. jcsd
  3. Aug 16, 2007 #2
    Ahh, I am wondering

    I track this eq from original eq



    I am able to get


    from this eq. I can get the right answer

    so, what's wrong in this eq.

    d= (y1*y2)/(2*n(y2-y1))

  4. Aug 16, 2007 #3


    User Avatar
    Science Advisor

    Please do NOT post the same question in more than one forum.
  5. Aug 16, 2007 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Why don't you explain what this equation represents and define the terms? What are n1 and n2? y1 and y2?
  6. Aug 16, 2007 #5
    Sorry mate.

    Now, I've already known.

    Thank you.
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