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Newton's Rings questions

  1. May 28, 2010 #1
    FG10_P11_NewtonsRings1.jpg

    So we know Newton's rings. I have two concrete questions:

    1) Why is the center point black? I quote from my book: "Because there is no path difference and the total phase change is due only to the 180° phase change upon reflection, the contact point is dark." I'm not quite sure what they mean, they either suggest:
    a) at the contact point there is one beam reflecting without a phase shift and one beam going out of the curved glas but immediately bouncing back WITH a phase shift and they cancel each other;
    b) nothing happens at the contact point, there is just a 180° phase shift at the VERY top;
    Both explanations seem wrong... a: then if you take two flat sheets of glas and stick them onto each other, you should get destructive interference everywhere; b: just take a sheet of glas and you see nothing because all the incident light receives a 180° phase shift (in this one there isn't even anything to cancel with, so it makes the least sense of all...)

    2) How come, in analyzing the circles, we can ignore the reflection on the very top layer? In some pictures some circles are very dark, so is there really no reflection on the top surface? Did they make the top surface non-reflecting or something?

    Thanks very much,
    mr. vodka

    EDIT: Am I right in presuming that --opposite to experiments like that of Young-- interference patterns like Newton's Rings or those formed by thin films are dependent on the angle at which you look at them?
     
    Last edited: May 28, 2010
  2. jcsd
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