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Homework Help: Single-slit Diffraction Question Pls help

  1. May 31, 2009 #1
    1. The problem statement, all variables and given/known data

    Monochromatic light of 585 nm is shone on a slit of width 8.0 x 10^-2 mm and the interference pattern is produced on a screen 1.8 m from the source. What is the width of the first-order bright fringe?

    2. Relevant equations


    3. The attempt at a solution
    PD=? Im not sure what n would be.. thats my main problem
    wavelength= 5.85 x 10^-7 m
    L= 1.8 m
    w= 8 x 10^-5 m

    When I used n=1 wavelength, i got the right answer, but n=1 is the first order dark fringe.. can someone please explain to me this.. i would just like to know what n would be.. thankyou any help is muchly appreciated.

    thankyou xie xie ni mm goi!
  2. jcsd
  3. May 31, 2009 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    Why do you think that?

    Doesn't n refer to the nth maximum?
  4. May 31, 2009 #3
    single slit diffraction equations lead to dark fringes, however as the separation between two dark fringes and two bright fringes are the same, it does not make any difference
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