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Homework Help: Spherical cavity electric field

  1. May 23, 2007 #1
    A positive charge Q = 2800.00 C is uniformly distributed over the volume of a sphere of radius R = 6.00 m. Suppose a spherical cavity of radius R/2 is cut out of the solid sphere, the center of the cavity being a distance R/2 from the center of the original solid sphere (see figure). The cut-out material and its charge are discarded. What is the magnitude of the electric field produced by this new charge distribution at point P, a distance r = 19.00 m from the center of the original sphere?

    so i am going to use the principle of superposition


    inorder to find E i must find the charge and i can do so by using porportions


    that is 28000/904.7787=Ql/113.0973 and Ql=3500

    so i am going to use the formula E=KQ/R^2 for both big a little spheres

    and i have E=(K28000/19^2)-(K3500/16^2)

    with this i am not getting the right solution...please help me find where i am going wrong
  2. jcsd
  3. May 23, 2007 #2

    Doc Al

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    Staff: Mentor

    Looks OK to me. Where is point P with respect to the two spheres? (Since we don't have the diagram, it's up to you to describe it carefully.)
  4. Jul 1, 2010 #3
    did you ever figure this out?
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