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Homework Help: Young's double slit

  1. Feb 6, 2010 #1
    1. The problem statement, all variables and given/known data
    1. What will happen if we use white light as the source of young's double slit experiment?
    2. If the experiment is done in water, what will the effect to the yn? yn is the distance of nth fringe from center fringe.

    2. Relevant equations
    d sin θ = nλ
    d y/D = nλ

    3. The attempt at a solution
    I'm not really sure. Will we get some colors of light on the screen like dispersion by prism? If yes, why? Is it because white light consists of several color so each of the color will make different interference pattern because of the difference of wavelength?

    The value of yn will decrease because the wavelength will decrease. Am I right?


    NB : Is there a term for yn? We call the separation of adjacent fringes is fringe separation, so what is the term for the distance of nth fringe from center bright?
  2. jcsd
  3. Feb 6, 2010 #2
    Your answer to number one is correct,each wavelength will produce its own pattern and all the patterns will overlap.
    Your answer to number two is correct.
    If you know the equation for fringe separation you can easily answer the question you set in your footnote.
  4. Feb 6, 2010 #3
    Hi Dadface

    Equation for fringe separation :

    w = λD/d, but what is the relation to the term of yn?

  5. Feb 6, 2010 #4
    Hello songoku, distance from centre of the first order fringes =1*w,distance from centre of second order fringes=2*w and so on.For the nth order fringes distance =nw.
  6. Feb 6, 2010 #5
    Hi Dadface

    hm...maybe I don't state the question clearly because of my poor English. I'm not looking for the formula, but I want to know what the "name" for yn is. Like what I wrote before :
    the separation of adjacent fringes = fringe separation

    yn = distance from center bright to nth fringe = ....? maybe it is called nth fringe?

  7. Feb 6, 2010 #6


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    Homework Helper

    The formula for yn is given by
    yn = n*d*lamda/D, where d is the slit width and D is the distance between slit and the screen.
    Now what happens to the wavelength when the light travels from air to water?
  8. Feb 7, 2010 #7
    You can call it the nth bright fringe.To be more precise the central fringe is called the "zero order fringe".The two bright fringes either side of that are called the "first order bright fringes"and so on.Your question was referring to one of the "nth order bright fringes"
  9. Feb 7, 2010 #8
    Hi rl.bhat and Dadface

    Thanks a lot !!
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