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Homework Help: Constructive wave interference problem

  1. Mar 28, 2009 #1
    1. The problem statement, all variables and given/known data

    A sheet of glass is coated with a 505nm thick layer of oil (n = 1.42).

    For what visible wavelengths of light do the reflected waves interfere constructively/destructively?

    2. Relevant equations

    For constructive interference


    For destructive interference


    3. The attempt at a solution

    for constructive

    2*1.42*505/(3 or 4) (since m=3 and 4 will give me a visible wavelength) lamba = 717 nm, 478 nm

    for destructive

    2*1.142*505/(3 or 4 + 1/2) (since m=3 and 4 will also give me a visible wavelength) lamba = 574, 410 nm

    HOWEVER, they are wrong... so im completely clueless of what to do next.. help please >.<
  2. jcsd
  3. Mar 28, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Re: Interference

    Hint: How does the index of refraction of the oil compare to that of the glass. Does it matter?
  4. Mar 28, 2009 #3
    Re: Interference

    glass is supposed to have a higher index of refraction.. yes it matters...
  5. Mar 28, 2009 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Re: Interference

    Hmmm... in that case your solution looks fine to me.
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