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Homework Help: Wave optics interference and diffraction

  1. May 9, 2006 #1
    Imagine you are trying to measure the width of a single strand of spider web. You have fastened the web to the slide, only rather than mounting the strand vertically as you did with the hair, you have mounted it horizontally. You illuminate the strand with a 650nm laser and project the resulting interference patter onto the wall where you have fastened this piece of paper such that the interference patter strikes within the box below. Given that the strand is 65 um wide and is loacated 2 meters from the wall, draw the resulting interference pattern you would see in the box provided. Draw the pattern to scale in the correct orientation. Include only the m= -2, -1, 0, 1, 2 maxima (bright spots). Indicate the distance between each adjacent maximum.

    Okay i have no idea how to do this! someone please help!! thank you...
  2. jcsd
  3. May 9, 2006 #2

    Chi Meson

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    This diffraction pattern will follow the same logic as the diffraction pattern created by light shining through two slits.
  4. May 9, 2006 #3
    thank you!!!
  5. May 10, 2006 #4


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    A Single obstruction is more like a single opening than like a double opening.

    The angles of course are vertical, with the central max in the middle of the shadow.
    (see "Poisson's spot" in the index for nice photos)
  6. May 10, 2006 #5

    Chi Meson

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    Hmm you're right. I just did the experiment with my own hair. The central fringe is twice as wide as the higher order fringes which indicates that it is following the (counterintuitive) logic of the single gap diffraction pattern. (counterintuitive in that you get destructive, not constructive, interference at the point where light from the two sides of the barrier have a difference in path length of exactly one wavelength).

    Gosh I hope tink comes back!:blushing:
  7. May 10, 2006 #6
    don't worry i figured it out! thanks again!
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