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Homework Help: Electricity Problem

  1. Feb 23, 2005 #1
    Two conducting spheres have identical radii. Initially they have charges of opposite sign and unequal magnitudes with the magnitude of the positive charge larger than the magnitude of the negative charge. They attract each other with a force of 0.162N when separated by 0.3m. The spheres are suddenly connected by a thin conducting wire, which is then removed. Note the spheres repel each other with a force of 0.041. What is the magnitude of the postive charge? Answer in units of C.

    I tried using the formula Fe=(kq1q2)/(d squared) but i was unsuccessful... :blushing:
  2. jcsd
  3. Feb 23, 2005 #2
    You have the right idea, you know before the wire:
    Fe=(k*qb1*qb2)/(d^2) = -0.162N
    qb1 is the charge on sphere one before the thin wire is attached. Sphere one will also be the posatively charge sphere. I am using negative force to mean attractive.
    After the thin wire is attached:
    Fe=(k*qa1*qa2)/(d^2) = 0.041.

    After the sphere touch they equaly distribute the charge over both spheres so.
    (qb1+qb2)/2 = qa1 = qa2

    Does the problem make more sence now?
  4. Feb 23, 2005 #3
    It's more clear to me how to do this problem...
    After the thin wire attached, I calculated that qa1=qa2=6.4 times 10^-7.
    Then, I assume you can use math to calculate qab, right? I'm not sure how though, as my math skills aren't that good either.
    Thanks for helping!
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