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Intensity - Double slit diffraction

  1. Oct 2, 2012 #1
    Hello. I have been studying interference and diffraction and one doubt has appeared. When you consider the double slit experiment forgeting the effects of diffraction you get the following equation for intensity


    where d is the distance between the slits.
    For the single slit diffraction we get



    where a is the width of the slit.

    Then for the double-slit case considering diffraction we get


    My doubt raises when i consider the two limit cases:
    1.For a/λ going to 0 the expression becomes that of the interference-only case.
    2.But when we consider d=0(the distance between the centers of the slits) the expression obtained is


    which is different from that of the single slit case although doing d=0 we are turning two slits of width a in one slit of width a.

    My thoughts trying to solve this problem have considered that maybe i am taking the limit case wrong (although i havent found where) or some expression for the intensity is wrong.

    Thanks in advance for your attention, expecting a good answer...

    PS.:I also apologize in advance for any mistake in my english writing...Brazilian here.
    Last edited: Oct 3, 2012
  2. jcsd
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