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Homework Help: Single Slit Problem

  1. Sep 15, 2008 #1
    1. The problem statement, all variables and given/known data
    Light from a helium neon laser with wavelength 633nm is incident on a single slit. What is the largest slit width for which there are no minima in the diffraction pattern?

    2. Relevant equations

    3. The attempt at a solution

    For single slit diffraction, asin(theta)=p*lambda, where a= slit width, and p= 1,2,3...

    So I know that when the slit width is smaller than the wavelength, no minima occur, but ?
    what about when it is equal?

    I'll try out some numbers: say the slit width is 6.33e-7 m, the same as the wavelength. Then I will find the angular position of the first minimum:

    theta has to be equal to 90 degrees, which I don't think can be possible. So the wavelength has to be less than 633 nm.

    Is this correct?
  2. jcsd
  3. Sep 15, 2008 #2
    Actually, I think that when the slit width is equal to the wavelength, then the light spreads to fill the region behind the opening. Therefore, I think that the largest the wavelength can be is 633 nm.
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