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Homework Help: Finding slit seperation in two-slit experiment

  1. Nov 4, 2012 #1
    1. The problem statement, all variables and given/known data

    Light from a He-Ne laser ([itex]\lambda[/itex] = 632.8nm) strikes a pair of slits at normal incidence, forming a double-slit interference pattern on a screen located 1.50 from the slits. The figure shows the interference pattern observed on the screen

    What is the slit separation?

    2. Relevant equations

    d*sin([itex]\theta[/itex]) = m*sin([itex]\lambda[/itex])
    y = L*sin([itex]\theta[/itex])

    3. The attempt at a solution

    I know i can solve this problem if i just find sin([itex]\theta[/itex]) but this is where i'm getting stuck.

    Also, does the diagram tell me anything important? i thought maybe by dividing the 23mm by 4, i could get y (the distance between each bright fringe) but that proved to be fruitless when i tried solving for sinθ using 0.023/4 = 1.5sinθ but that didn't give me the correct answer for d.

    nevermind. i figured this out.
    Last edited: Nov 4, 2012
  2. jcsd
  3. Nov 5, 2012 #2


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    Homework Helper

    The formula should be d*sin(θ) = m*λ.
    Draw your diagram with one line horizontal from the slits to a bright central maximum and another line at angle θ to the next bright spot, separated from the first by x. You can figure out x from the given diagram and then you can get the hypotenuse in the new diagram using the Pythagorean theorem. Use the formula to solve for the slit separation distance d.
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