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Work Done by an Insulating Sphere on a test charge

  1. May 20, 2013 #1
    1. The problem statement, all variables and given/known data

    An insulating sphere of radius 0.240 has uniform charge density 6.50×10−9 . A small object that can be treated as a point charge is released from rest just outside the surface of the sphere. The small object has positive charge 4.10×10−6

    How much work does the electric field of the sphere do on the object as the object moves to a point very far from the sphere?

    2. Relevant equations

    3. The attempt at a solution

    I tried to use kQq/r to find the work done but I'm honestly very lost about where to start.

    Any help is extremely appreciated, thanks.
  2. jcsd
  3. May 20, 2013 #2


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    You've got the right formula, now use it. You can treat the sphere as a point charge concentrated at the center of the sphere. What's the total charge of the sphere?
  4. May 21, 2013 #3
    would it be the charge density multiplied by the surface area of the sphere?, so 4/3pir^3(6.5x10^-9)?
  5. May 21, 2013 #4


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    4/3pir^3 is the volume of the sphere, not the surface area. But I still think that's the correct thing to do. If it's an insulating sphere they probably gave you the volume density not the surface density.
  6. May 21, 2013 #5
    bleh stupid me, appreciate all the help Dick :)

    Close please solved
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