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Homework Help: Optics / interference in thin films

  1. Sep 1, 2008 #1
    1. The problem statement, all variables and given/known data
    A soap bubble n=1.33 is floating in air. If the thickness of the bubble wall is 115 nm, what is the wavelength of the light that is most strongly reflected

    2. Relevant equations

    3. The attempt at a solution
    most strongly reflected = constructive interference
    t=115 nm
    lambda = unknown
    n = 1.33
    assumption m=0
    plug and chug to get lambda

    so I got the answer, but I was confused on why we make the assumption that m=0, couldn't m technically be any integer number? Do we just automatically assume that m=0 for "most strongly reflected" if a specific desired wavelength is not given?

    thank you!!
  2. jcsd
  3. Sep 1, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    Yes, strictly speaking the question should have said, what is the longest wavelength that is most strongly reflected.
    However if you use m>0 you will get wavelengths that are outside the visible band.
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