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Distance between two bright fringes

  1. Apr 16, 2012 #1
    1. The problem statement, all variables and given/known data
    A new experiment is created with the screen at a distance of 2.2 m from the slits (with spacing 0.12 mm). What is the distance between the second order bright fringe of light with l = 683 nm and the third order bright fringe of light with l = 400 nm? (Give the absolute value of the smallest possible distance between these two fringes: the distance between bright fringes on the same side of the central bright fringe.)



    2. Relevant equations
    sin∅=mλ/d


    3. The attempt at a solution
    For first wavelength,
    ∅=arcsin(2(683*10^-9)/1.2*10^-4)
    ∅=.65
    Setting up triangle, I get D_683=2.2tan(.65)=.0249

    For second wavelength,
    ∅=arcsin(3(400*10^-9)/1.2*10^-4)
    ∅=.57
    Setting up triangle, I get D_400=2.2tan(.57)=.0219
    I thought that D_683-D_400 should give me the distance between the two fringes but my answer of .003m keeps getting rejected. I have done this problem over and over and I cannot for the life of me figure out what I am doing wrong.
     
  2. jcsd
  3. Apr 16, 2012 #2
    The math looks pretty solid to me. Not quite sure why that answer would be rejected. Sorry if that's not helpful.
     
  4. Apr 17, 2012 #3
    Might want to find the width of each fringe too, it does state smallest possible value, but with your calculation it is not smallest possible value.
     
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