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Homework Help: Maximum slit width of double slit

  1. May 9, 2014 #1
    1. The problem statement, all variables and given/known data


    Estimate maximum slit width of a double slit.

    2. Relevant equations

    3. The attempt at a solution

    Letting the slit width be a,

    The intensity profile of such a system is:

    [tex]I = I_0 sinc^2\left( \frac{Nkasin \theta}{2} \right) cos^2\left( \frac{kd sin\theta}{2} \right)[/tex]

    I suppose the maximum slit width is when a = d? Such that all the interference maxima coincides with the minima from diffraction envelope. But physically this would mean that both slits collapse into one..
  2. jcsd
  3. May 9, 2014 #2
    The question is not about the width of the double slits. - It is about the width of the source slit (that's where the light comes from to begin with even before reaching the double slits.
  4. May 9, 2014 #3
    Hmm, that's interesting. But the first thought is that why would it matter? If the beam is really wide, it would get diffracted the normal way.
  5. May 10, 2014 #4
    It matters because it determines whether or not the incoming light is coherent.
  6. May 11, 2014 #5
    Well, but there is no path difference before approaching the slit, so why would it matter?
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