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Homework Help: Diffraction Grating Multiple Choice Questions

  1. Feb 27, 2007 #1
    Hey, I have to answer the following multiple choice questions ... its relevant to my exam which is day after tomorrow. Can anyone please tell which options should be the answers and why... I don't have any clue about these. So please don't delete this post ... instead please help me to pass the exam. I'll never forget your guy's help. Thanks

    Covering up one of the slits on a double slit experiment would have which of the following effects?

    a. The larger pattern would get slightly smaller
    b. The small pattern within the larger pattern would get slightly larger
    c. The larger pattern would disappear
    d. The smaller pattern within the larger pattern would disappear
    e. The small angle approximation would no longer be valid

    The Huygens-Fresnel principle tells us to pretend that each point of a wavefront in a slit or aperture is a point source of light emitting a spherical wave. Is this true only for points inside the slit? What if there is no slit? The Huygens-Fresnel principle really applies

    1. to any point anywhere in a beam path.
    2. to any point in a beam path where matter is present.
    3. only in slits or apertures.

    If the Huygens-Fresnel principle applies to any point anywhere in a beam path, why doesn’t a laser beam without any slit spread out in all directions?

    1. Because all waves that spread interfere destructively.
    2. It does spread, but the spread is so small that we normally don’t notice it.
    3. We can’t apply the Huygens-Fresnel principle anywhere but in slits and apertures.

    Light waves from two point-like sources arrive at the circular aperture of a telescope simultaneously. The telescope will resolve the two sources if which of the following conditions is satisfied?

    1. the Fresnel approximation
    2. the Fraunhofer approximation
    3. the Huygens-Fresnel principle
    4. the Rayleigh criterion
    Last edited: Feb 27, 2007
  2. jcsd
  3. Feb 27, 2007 #2
    What do you think the answers might be and why? :smile:

    Some things to consider:

    1) What light pattern does a single slit produce?
    2) Does your textbook show a sketch illustrating the Fresnel Huygens principle, and if so, what does it show?
    3) Is the end of the laser cavity a kind of circular slit?
    4) What does it really mean to be able to "resolve" two points?
  4. Feb 27, 2007 #3
    I already said that I don't know anything about this stuff. :cry: :cry:
  5. Feb 27, 2007 #4
    Then if you don't try, you'll deserve to flunk. :smile:

    Try to answer the questions I posed, one by one.
  6. Feb 28, 2007 #5
    thanks anyways.
  7. Feb 28, 2007 #6


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    Do you have a textbook? Have you tried researching it on the web or in a library?
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