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Homework Help: Destructive interference and fringes

  1. Nov 26, 2007 #1
    I am looking for the distance between the 2nd and 3rd DARK fringes on a screen.

    Monochromatic, coherent light is shone through 2 slits a distance d apart.

    Wavelength is L. Distance between grating and screen is R.

    The formula I am using is: [(R(5/2)L)/d - (R(3/2)L)/d]

    I am using 5/2 and 3/2 since these should be the number of wavelengths for destructive interference for the 3rd and 2nd fringes respectively.

    The formula doesn't seem to be working though. Where have I gone wrong????
     
  2. jcsd
  3. Nov 26, 2007 #2
    BUMP!:approve:

    Come on guys. Any help? I really need to get this sorted today.
     
  4. Nov 26, 2007 #3

    Doc Al

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    Staff: Mentor

    Your formula looks OK to me. Why do you think its wrong?
     
  5. Nov 26, 2007 #4
    I feel like an idiot.


    Ah it was a classic unit conversion error!:blushing:


    Thanks tho!
     
  6. Nov 26, 2007 #5

    Doc Al

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    D'oh! (Been there, done that.)
     
  7. Nov 26, 2007 #6
    Could you help me with my final part so?
     
  8. Nov 26, 2007 #7

    Doc Al

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    Final part of what?
     
  9. Nov 26, 2007 #8
    I have 2 questions relating to light. This is one. I have posted the other. It is do with interference in a film.

    Please excuse the posts in the thread. The first one relates to the question.
     
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