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Homework Help: Singe Slit Diffraction

  1. May 25, 2005 #1
    Hey, I have a problem here involving single slit diffraction, and it's stumped me.

    A single slit is illuminated with a 660-nm light, and the resulting diffraction pattern is viewed on a screen 2.3 m away. If the linear distance between the first and second dark fringes is 12 cm, what is the width of the slit?

    I want to use this formula to start me off:

    y= L tan (theta)

    But what value of y should I use? It can't be 12 cm, because that's defining the distance between those two dark fringes, not their distance to the central bright fringe.

    Any ideas?
  2. jcsd
  3. May 26, 2005 #2


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    Homework Helper

    The notation is a bit different, but take a look at the diagram and the equation here.


    You have two different y values corresponding to two different values of m, and all you know is the difference between the y values. You can use the equations to take the difference between the y values for the two m values and relate that difference to the distance to the screen and the slit width.
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