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Homework Help: Very hard physics problem!

  1. Dec 4, 2013 #1
    1. The problem statement, all variables and given/known data

    You are coating a glass lens of index of refraction 1.6 with a film of material of index of refraction 1.7. You start with the thinnest film possible that creates a strong reflection for 610 nm light. You gradually increase the film thickness until you again get strong reflection. What is the thickness of the film now?

    2. Relevant equations

    Wavelength in film = wavelength in a vacuum / index of refraction of film

    610 nm / 1.6 = my answer? Not sure if this is correct.

    3. The attempt at a solution
    Just need to be pointed in the right direction! Really am not sure where to start for this problem. Any help would be really nice!
  2. jcsd
  3. Dec 4, 2013 #2


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    Probably not.

    It's fairly obvious you're just guessing. I mean, how do you know the answer isn't 610 nm/1.7? Or maybe it's some combination of 1.6 and 1.7. Or maybe it has absolutely nothing to do with the indexes of refraction. Why do you think it does? (It could be the information is superfluous.)

    Think about what's going on here. What's happening when get a strong reflection?
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