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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
    2nt=(m+0.5)(lambda)


    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

    mgb_phys

    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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