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Homework Help: Double Slit Wave Interference Question

  1. Jan 21, 2012 #1
    1. The problem statement, all variables and given/known data

    Blue light (λ = 482 nm) is directed through parallel slits separated by 0.15 mm. A fringe pattern appears on a ascreen 2.00 m away. How far from the central axis on either side are the second order dark bands?

    λ = 4.82 x 10-7 m
    d = 1.5 x10-4 m
    L = 2.00 m
    m = 2
    y= ?

    2. Relevant equations

    sin θ = (m + 0.5) λ/d
    y = L tan θ

    3. The attempt at a solution

    I used m = 2 (second order dark bands) and used the first equation which gave me the angle formed between the central axis and the second order dark band, which came out to be 0.46 degrees. I then used the second formula, which is the formula for the distance between the central bright fringe and any point on the screen, which gave me 0.016 m or 16 mm. The textbook says 38 mm, but I'm sure I've done it correctly
    Last edited: Jan 21, 2012
  2. jcsd
  3. Jan 21, 2012 #2


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    Homework Helper

    Your calc checks out.
    I took m = 0 as being the first order dark fringe and m = 1 as the second order, which works out to 9.6 mm.
    I don't see any way to get 38!
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