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Homework Help: Calculating Electric Field of Insulating Sphere

  1. Sep 5, 2011 #1
    1. The problem statement, all variables and given/known data
    A charged paint is spread in a very thin uniform layer over the surface of a
    plastic sphere of diameter 12.0 cm, giving it a charge of -35.0 mC. Find the
    electric field (a) just inside the paint layer, (b) just outside the paint layer, (c)
    5.00 cm outside the surface of the paint layer.

    r= .06 m
    q =-35e-6

    2. Relevant equations

    E= k*(q/r^2)

    3. The attempt at a solution
    Here is where my problem is. I'm not sure how to start it. In particular, I'm not sure what how to deal with the charged paint. Here are some questions I have that I would appreciate help with:
    1-The sphere is plastic, so I treat it as an insulator. When the paint is applied and gives it the -35 mC charge, is that charge spread uniformly throughout the sphere?
    2-Since the paint gave a -35 mC charge, does that mean the paint itself is +35 mC?
    3-What numbers am I suppose to use for parts A and B?

    Again, I feel like there is some trick with this paint thing that is eluding me and would be grateful for any direction.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 5, 2011 #2
    This means that the distribution of charge is uniform throughout the sphere (answer to (1) )

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