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Diffraction Grating problem

  1. Apr 10, 2004 #1
    Question: A set of narrow vertical slits is located a distance D from a screen. The slits are equally spaced and have the same width. The intensity pattern in the figure is observed when light from a laser passes through the slits, illuminating them uniformly. The screen is perpendicular to the direction of the light.

    Calculate the width of the slits, in micrometers.

    You are given the following data: Distance to the screen = 2.77 meters; Wavelength of light = 0.420 micrometers; Distance between tick marks on the intensity figure = 1.60 cm (The figure has the generic diffraction grating light pattern, with tick marks occurring between each maxima)

    Maxima occur at sin theta = m lambda / d (where m is the order, lambda is the wavelength of light, and d is the distance between slits)

    first.. I find out what theta is.. i can find this by
    tan theta = (.016m)/(2.77m)
    tan theta = .0057761
    theta = .33095 degrees

    plugging into the maxima formula,
    sin theta = m lambda / d
    sin (.33095) = 1 (.420x10^-6) / d
    d = 7.27x10^-5m = 72.7 micrometers

    72.7 micrometers is incorrect. Anyone know where I went wrong?

  2. jcsd
  3. Apr 11, 2004 #2
    Any thoughts on this problem?

    It seems so straight forward that I can't see where I may have gone wrong..

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