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Homework Help: Young double slit experiment

  1. Nov 17, 2005 #1

    i am doing a work sheet on the title of this thread and i do not have the answer sheet for the questions so can some one please go through my answers and see if i am correct

    Young used a monochromatic light source
    a) wat does this mean?
    my ans: light of a single wavelength

    b) how did he achieve this?
    my ans: by using sunlight

    c)wat is the purpose of the single slit?
    my ans: so that only light from the single slit will reach the double slit

    d)when does destructive interference occur?
    when the wavelength is 1/2 of the wavelength of the bright fringes
  2. jcsd
  3. Nov 17, 2005 #2

    Doc Al

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    Staff: Mentor

    That's the correct meaning of monochromatic.

    Sunlight is not monochromatic.

    Well, yes, but why is that important? (The key is that it keeps the path length the same for light hitting the double slits.)

    Not sure what that means. Hint: What must be the path length difference between light from each slit arriving at a point on the screen so that there is destructive interference?
  4. Nov 18, 2005 #3
    thank u doc

    for the qn 2 , wat then qualifies as a monochromatic light?

    for the last qn, i mean to say the path difference between the 2 sources must be 1/2 wavelength
  5. Nov 18, 2005 #4

    Doc Al

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    I don't know what Young did in his orginal experiments to get a monochromatic source, but he could have used a filter or a prism to select a single wavelength. (If you don't use a monochromatic source, then you'll get overlapping fringes from each wavelength.) Nowadays, getting a monochromatic source is easy using lasers.

    Good. The path difference of the light from each slit must be 1/2 wavelength for destructive interference.
  6. Nov 18, 2005 #5
    I assume he used a sodium lamp - it's monochromatic enough (not coherent though - that doesn't mean it's impossible to do but it makes it bl--dy hard (speaking from experience here :cry: )
  7. Nov 18, 2005 #6


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    I believe Young did use sunlight in his original experiment.
  8. Nov 18, 2005 #7

    Doc Al

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    Absolutely. I just don't know what pains, if any, he took to select a particular wavelength.
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