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A shaft of light pass through the prism

  1. Mar 11, 2006 #1
    A shaft of light passes through a prism with refracting angle [tex] \theta [/tex] and refractive index [tex] n [/tex]. Let [tex] \alpha [/tex] be the deviation angle of the shaft. Demonstrate that if the shaft of light passes through the prism symetrically the angle [tex] \alpha [/tex] is the least?
  2. jcsd
  3. Mar 11, 2006 #2
    The least in regards to what?

  4. Mar 11, 2006 #3

    I suppose that [tex] \beta [/tex] is the refracting angle

    I think that it try to proove that [tex]\beta[/tex] is equal to [tex] \theta [/tex] angle [tex] \alpha [/tex] will become the least.

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  5. Mar 12, 2006 #4


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    Homework Helper

    "passes through symmetrically" means that the path inside the prism
    is parallel to the face of the prism that isn't used as a window ...
    that is, theta_glass on face 2 = - theta_glass on face 1.

    You'll probably want to assume an "apex" angle for the prism
    and recall that the interior angles in a triangle sum to 180,
    to relate the theta_glass on face 2 to the theta_glass on face 1.

    With the deflection angle as a function of theta_glass, set the derivitive =0.
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