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Homework Help: Young's double slit experiment

  1. Aug 24, 2014 #1
    1. The problem statement, all variables and given/known data
    In a Younf's double slit experiment , the intensity of light at the centre of fringe pattern is I. If one of the two identical slit is now covered , the intensity at the cnetre ANS is 0.25I.

    2. Relevant equations

    3. The attempt at a solution
    In my opinion, it should be 4I. because the light ray is now concentrated at smaller area, but i know that intensity = power /area . As the area is decreased is decreased , the intensity should increase , assuming the power is constant.
  2. jcsd
  3. Aug 24, 2014 #2


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    Gold Member

    If you check against diffraction formulas, you'll see that the answer is [itex] \frac 1 4 I=0.25 I[/itex].
    But if you want arguments using density considerations, I should say that when you have two slits open, there is interference which means you have dark and bright bands and so the energy coming from the source has less places to be at which means greater density in those places than when you have only one slit open where light has all the wall to be at.
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