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Homework Help: Young's double slit and interference maximums

  1. Nov 21, 2008 #1
    1. The problem statement, all variables and given/known data
    In a Young's double slit experiment the width of each slit is a, the distance between the centers
    of the slits is d, and the 10th interference maximum to the right of the central maximum is the first
    missing maximum. a) Find the ratio of the slit separation distance to the width, d
    b) Find the number of interference maximums across the central diffraction maximum.
    c) Find the ratio of the intensity of the 5th interference maximum relative to intensity of the
    central maximum.

    2. Relevant equations
    phi = (2pi / lambda) * d * sin(theta)
    beta = (2pi / lambda) * a * sin(theta)

    3. The attempt at a solution
    (a) I see that the ratio d/a is phi/beta, but how do I determine the value of phi and beta? All I can think of is that the 1st minimum occurs at beta = 2pi, but I'm not sure how that would relate here.
    (b) No idea on this one
    (c) There's a long equation for I that relates it to I_o. It also includes cos^2 (phi/2) and also sin(beta/2), and is too long and I'm not sure how to write it here. I can figure this out I think if I know the value of either phi or beta, and then use the d/a ratio from part (a) to find the other value. Once I have those 2 I can use the equation to relate the 5th interference maximum intensity to I_o (central max intensity).

    Some explanations will also be greatly appreciated!
  2. jcsd
  3. Nov 21, 2008 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Your textbook should have an equation for the intensity of a single-slit diffraction pattern. You will need that.

    There should also be an equation for the interference maximums.
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