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Homework Help: Charge at Equilibrium Exercise, please help.

  1. May 12, 2007 #1
    Please help with the following exercise:

    Two conductor spheres with radius R and 2R are at a great distance one from the other. We put a charge of Q=+1.7C on the smaller sphere, and then we put them in contact with a conductor thread. Determine what charge the spheres will have at equilibrium. What would not work in our reasoning if the two spheres weren't at a great distance one from the other?

    I don't know what relation there is between what we are trying to find and the radius of the sphere. I know that if the spheres had the same radius, the charge at equilibrium between the two would be +Q/2.
    I don't know what would not work if the spheres were close, maybe the electric field influencing the motion of charge? I have no clue, please help.

    Thank you.
  2. jcsd
  3. May 12, 2007 #2


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    That would infer that the electric field caused by the electric charge on either sphere does not appreciably affect the other charge on the other sphere. Think of an electric field, which must originate from a charge somewhere.

    Anyway, there is a conservation of charge!

    The charge starts on one sphere, and has a specific charge density.

    When the two spheres are connected by a conductor, the charge redistributes such that the charge density must be equal.

    So for the given charge, determine the apportionment of the total charge assuming the same charge density and surface area of each sphere.
  4. May 12, 2007 #3
    Thank you very much, your help was precious.
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