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Soap bubble

  1. May 2, 2016 #1
    1. The problem statement, all variables and given/known da
    A soap bubble 500 nm thick is illuminated with white light. The index of refraction of

    this unique soap film is 1.35 for all colors (no dispersion). a) What wavelengths are not

    reflected?

    2. Relevant equations

    2nt=mL
    2nt=m(L/2)
    3. The attempt at a solution
    for m=1 2(1.35)(500nm)=1350nm
    for m=2 =675nm
    am i doing this right? i do not really understand what the question is looking for.
     
  2. jcsd
  3. May 2, 2016 #2

    Simon Bridge

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    Please explain your reasoning.
    ... then you are probably not doing it right.
    Even if you got the right answer, it would only be by accident.

    Why would some wavelengths not get reflected off the soap bubble?
     
  4. May 3, 2016 #3
    If they get absorbed they would not be reflected right? But I don't know how to translate this
     
  5. May 3, 2016 #4

    Simon Bridge

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    Not quite: the light does not have to be absorbed.
    You have probably just done a section on thin films. Recall that it depends on interference: the reflected ray off the bottom (inner) surface of the bubble interferes with the reflected ray off the top (outer) surface. Also recall that reflection may involve a phase change.

    If you missed it in class here's a crash course:
    http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/thinfilm.html

    You can find other examples online under "thin film physics".
     
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