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Homework Help: Finding Expected Lateral Displacement From a Risley Prism

  1. Sep 16, 2014 #1
    1. The problem statement, all variables and given/known data
    Find the expected lateral displacement for a spot of light at a power of [itex]6^{∆}[/itex].

    Distance from prism to where displacement was measured (b) = 62.2cm.

    The following displacements (x) were measured from the power given on the knob of the prism:

    [itex]3^{∆}[/itex] = 1.80cm
    [itex]6^{∆}[/itex] = 3.51cm

    2. Relevant equations

    P = 100[itex]\frac{x}{b}[/itex]

    If prisms are at 90° to each other, then resulting power will be 2P (with appropriate displacement). If prisms are at any other angle [0°,90°) then resulting power is 2Psinθ where θ is the angle between the two prism.

    3. The attempt at a solution

    [itex]6^{∆}[/itex] = 100[itex]\frac{x}{62.2cm}[/itex]

    x = 3.73cm

    This is comparable to what I recorded, however I'm unsure then why I was told to record the [itex]3^{∆}[/itex] reading and if the 2P or 2Psinθ parts were needed.
  2. jcsd
  3. Sep 16, 2014 #2


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    Hello Pythia, and welcome to PF.
    Am I right in reading ##6^{∆} ## as ##6^\circ## (six degrees) ?

    It is rather difficult for an outsider to get an idea of what this is about. Could you post some more info, and perhaps a sketch of the situation ?
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