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Derivation of the equation in doube slits

  1. Aug 21, 2007 #1
    Hi, can someone provide me with a simple derivation of the formula: x=λD/a[/B]
  2. jcsd
  3. Aug 21, 2007 #2


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    Sorry - you have to do a bit more than that.
    Start with explaining what the terms in the equation mean and draw a diagram for yourself - this will help you understand.
    When you have tried to find an answer we can help!
  4. Aug 22, 2007 #3
    oh boy! well... x=slit inteference, λ=wavelength of electromagnetic wave, D= distance between slit and board and a=difference in length of the 2 slits. I dun really know how to draw a diagram online so i will try my best to explain what im doing.

    I would find through pythogaras theorem the difference in the distance to the exact same spot in the board from both slits and through an approaximation in binomial theorem, i arrived at (a^2+2ab)/D where b is the perpendicular distance from the horizontal of the slit to the point of inteference point of concern.

    After which, calling the above difference in distance Y, i used a proportionality method which equated λ/Y=x/a.

    but sadly i did not get the answer, it is quite vexing any help?
  5. Aug 22, 2007 #4


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    Because the angle is so small you can use x = sin x (x in radians) which helps with the derivation and then you are just trying to find the angle at which the difference in path is 1 wavelength.
    I think you are over complicating it ! see here for diagram
    http://www.matter.org.uk/schools/Content/Interference/formula.html [Broken]
    Last edited by a moderator: May 3, 2017
  6. Aug 22, 2007 #5


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