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How would I do this problem?

  1. Feb 27, 2004 #1
    Question: Find the solid angle subtended at the origin by a thin circular disk of radius a, whose cente is a distance b from the origin and where the normal to the disk is parallel.

    Do I have to find the center of mass to solve this question?
     
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  3. Feb 27, 2004 #2

    HallsofIvy

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    "the normal to the disk is parallel"?? Parallel to what?

    The problem would be relatively easy if the normal to the disk were directed at the origin. It's quite a bit harder if the normal is parallel to the xy-plane or parallel to the z-axis.
     
  4. Feb 28, 2004 #3

    Dr Transport

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    If the normal of the disk is parallel to the direction from the orgin, the incremental solid angle is defined by

    [tex] d\Omega = {dA_s}\over{r^2) [/tex]

    where the numerator is the surface area of the shape and the demoninator is the distance from the orgin. For a cylindrical plate the surface area would be [tex] \pi a^2 [/tex]. For your problem, the solid angle could be approximated by

    [tex] \pi {a^2}\over{b^2} [/tex].
     
  5. Feb 28, 2004 #4

    Dr Transport

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    should be

    [tex] d\Omega = {\frac{dA_s}{r^2}} [/tex]
     
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