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M-M experiment

  1. Jun 4, 2006 #1
    Let T1 be the time taken by a ray of light to make a return trip between two mirrors aligned parallel to the Earth’s assumed motion through the aether.Let T2 be the time taken by a ray of light to make a return trip between two mirrors aligned perpendicular to the Earth’s assumed motion through the aether.Which of the following statements (A. – D.) best describes the value of the ratio T1 / T2 as measured by Michelson and Morley?

    A. slightly less than one
    B. equal to one
    C. slightly greater than one
    D. significantly greater than one

    I would say B, since no interference pattern was observed; and C if the experiment were a success (ie if the ether existed)... the book says it's C...


  2. jcsd
  3. Jun 4, 2006 #2
    Got that from http://scienceworld.wolfram.com/physics/Michelson-MorleyExperiment.html

    Good point...I think it's B too since the concept of ether was eventually rejected and the speed of light is found to be constant regardless.
  4. Jun 4, 2006 #3

    A few corrections:

    1. Of course there was (is) interference pattern.

    2. The real problem is: does the interference pattern SHIFT when the interferometer is rotated 90 degrees? (MM expected the pattern to shift)

    In reality the pattern shifted but...much less than predicted by the theory employed by MM. SR predicts zero shift and the latter day MM reenactments converge towards zero.

    Relative to your problem, I would have to say that it is very badly put in your book. To a badly put problem there is no good answer.
  5. Jun 5, 2006 #4
    If you could allow me to ask something on top of that, is the speed of light a constant in every medium? I understand that it travels at 3X10^8 ms^-1 approx in vacuum but I would suppose it slows down in a medium like air or water?
  6. Jun 5, 2006 #5
    Yes, light travels at different speeds through different media. That's what causes refraction.
  7. Jun 5, 2006 #6

    Andrew Mason

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    At the risk of being picky, here, it is important to note that photons always travel at c. The light appears to slow down when passing through a medium because of the absorption and emission that takes place in the medium when the photon encounters atoms.

    As far as the question is concerned, I would say that the correct answer to this question is b. MM did measure a slight fringe shift that put the speed of the earth through the aether at less than a few km/sec. but they were expecting much more. The shift was not significant. So the most meaningful answer is b. See http://en.wikipedia.org/wiki/Michelson-Morley_experiment#The_most_famous_failed_experiment"

    Last edited by a moderator: Apr 22, 2017
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