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Homework Help: Optics: I do not understand what this question is asking!

  1. Dec 11, 2011 #1
    1. The problem statement, all variables and given/known data
    Call the irradiance at the center of the central Fraunhofer diffraction maximum of a single slit [itex]I_0[/itex] and the irradiance at some other point in the patterm I. Obtain the ratio [itex]I/I_0[/itex] for some point on the screen that is 3/4 of a wavelength farther from one edge of the slit than the other.


    2. Relevant equations
    Irradiance for single slit diffraction
    [tex]I=I_0sinc^2(β)[/tex]
    [tex]β=\frac{1}{2}kbsin\theta[/tex]
    [tex]k=\frac{2\pi}{\lambda}[/tex]
    b=slit size

    3. The attempt at a solution
    Well I know that when beta is equal to zero, the irradiance is at its maximum. But I do not know if this helps me or not. I honestly do not understand the question. 3/4 of a wavelength farther from one edge of the slit than the other? Don't I need the slit length? How can I make use of this information? Why does it say "than the other." What other point?

    I really want to understand this problem. If anyone can help me I would much appreciate it!
     
  2. jcsd
  3. Dec 11, 2011 #2

    Andrew Mason

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    Homework Helper

    Think of two coherent light sources, one at each edge of the slit. At a point that is 3/4 of a wavelength farther from one of those two sources than the other, how would the amplitude of the combined wave compare to the amplitude at a point where there was full constructive interference (maximum amplitude). How would the intensities be related? (ie how is intensity related to amplitude?).

    AM
     
  4. Dec 11, 2011 #3
    In other words you don't need a variable if you have a way to cancel it using the given information and perhaps setting up two equations or a ratio
     
  5. Dec 11, 2011 #4
    Ohh! Okay that makes sense now! Thanks guys, I will give it a shot tomorrow. (Just finished studying :p)
     
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