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Homework Help: This is a problem on electric current

  1. Feb 11, 2009 #1
    1. The problem statement, all variables and given/known data

    An isolated conducting sphere has a 10 cm radius. One wire carries a current of 1.000 002 0 A into it. Another wire carries a current of 1.000 000 0 A out of it. How long would it take for the sphere to increase in potential by 1200 V?

    2. Relevant equations


    3. The attempt at a solution
    tried using i= dq/dt
  2. jcsd
  3. Feb 11, 2009 #2
    You'll need to rearrange the following equation to find how much charge, [itex]q[/itex], the sphere will store when its surface potential is at 1,200 V.

    [tex]V_R=\frac{q}{4 \pi \epsilon_0 R^2}[/tex]

    You know the magnitudes of the inward- and outward-flowing currents, therefore you can calculate the net inward-flowing current. All you need to do next is work out how long it takes for this current to transfer charge [itex]q[/itex].
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