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Homework Help: Width of the slit

  1. Sep 12, 2014 #1
    1. The problem statement, all variables and given/known data
    Monochromatic light of wavelength 550nm is used to illuminate normally a narrow slit. A converging lens of focal length 50cm is used to focus the diffraction pattern onto a screen. If the seperation between the first minima is 10.0mm What is the width of the slit. The ans is 0.055mm.

    2. Relevant equations

    3. The attempt at a solution
    by using formula x= λD/ a ,
    i have 10x10^-3 = (550x10^-9) x ( 50x10^-2) / (a) ,
    i get my a = 0.0275mm ... What's wrong with my working?
  2. jcsd
  3. Sep 12, 2014 #2


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    Is this formula meant to give the distance between the two first-order minima or is it meant to give the distance between the central maximum and one of the first-order minima?
  4. Sep 13, 2014 #3
    I guess the op means the distance between two first min is x ?
  5. Sep 13, 2014 #4
    In the working above I assume the x is distance between two first minimum... Anything wrong with it?
  6. Sep 13, 2014 #5


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    x is the distance of any of the first minima from the central maximum.

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