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Homework Help: Find the charge density inside a solid insulating sphere?

  1. Sep 16, 2014 #1
    1. The problem statement, all variables and given/known data
    The electric field at a distance of 0.143m from the surface of a solid insulating sphere with radius 0.381m is 1630N/C .

    a) Assuming the sphere's charge is uniformly distributed, what is the charge density inside it?

    b) Calculate the electric field inside the sphere at a distance of 0.237m from the center.

    2. Relevant equations
    E1/E2 = r1/r2
    E = Cr

    3. The attempt at a solution

    a) I know that the electric field for part a can be found by using the formula E=Cr, so I can get C = 4278.22 N/(C*m). I know that the charge density is a factor of C, but I do not know the actual formula for it.

    b) This should be able to be solved with the ratio E1/E2 = r1/r2, and when I solve for E2 I get a result of 737.2 N/C. This result is not correct, but I am not sure if the problem is in my ratio.
  2. jcsd
  3. Sep 16, 2014 #2

    Simon Bridge

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    You can figure it out though. Hint: what are the units of charge density?

    Write out the equation for E1 and E2 separately, then find E1/E2.
  4. Sep 17, 2014 #3

    rude man

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    a) 1. figure out what total charge Q is for an E field at the specified location.
    2. Q = volumetric charge density x volume gives you charge density.

    b) 1. Use Gaussian surface.
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