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Thin Film Interference problem

  1. Dec 8, 2007 #1
    Hey guys, I was wondering if someone could explain to me when Thin Film Interference will produce constructive/destructive interference. I think I might understand it, but I'm not 100% sure and I have a test coming up soon. Any help would be great!

    Ok, so I know we have the equation:
    2t = m[tex]\lambda[/tex]

    where t, is the distance the thickness of the film, and [tex]\lambda[/tex] is the wavelength.

    Say we have...


    Where n1 = air, n2 > n1 and n2 > n3. So then would the part of the ray reflecting off n2, have a 1/2 [tex]\lambda[/tex] phase change? But the ray reflecting off of n3 would undergo no phase change?? Would this produce destructive interference?

    What about when n2 > n1, and n3 > n2. I'm guessing that both the ray that reflects off n2, and off n3 would both undergo 1/2 [tex]\lambda[/tex] phase change, so this would be constructive?

    Or is it reversed?
  2. jcsd
  3. Dec 8, 2007 #2

    Doc Al

    User Avatar

    Staff: Mentor

    You got it.
  4. Dec 8, 2007 #3
    Thanks :)
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