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Fresnel Double Prism equation

  1. Jan 23, 2005 #1


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    i need to deduce the Fresnel Double Prism equation, which states:

    d = 2a(n-1)alpha,

    according to the linked image.
    Fresnel Double Prism setup

    The distance between the constructed virtual objects S' and S'' is here called d. The distance from the light source to the prism is called a, the prism has two sides (common base) defined by the common apex angle alpha, and the refractive index n.

    Any help appreciated!!
  2. jcsd
  3. Jan 23, 2005 #2
    Hi jh,

    You probably know that for a single prism the deviation angle is given by
    The refraction' law in the incidence and emergence points (for very small angles) is
    and from these two equations you have now

    It is clear now that

    Because you have a double prism,
    and [tex]\delta_{tot}\cdot a[/tex] for the distance between the two points (images). ( [tex]A=\alpha[/tex])
    Last edited: Jan 23, 2005
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