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Homework Help: Charging an insulator problem

  1. Jan 27, 2009 #1
    1. i have the answer, but just dont understnad it
    A small metal ball is given a negative charge, then brought near (i.e., within a few millimeters) to end A of the rod. What happens to end A of the rod when the ball approaches it closely this first time?

    Select the expected behavior.

    X strongly repelled
    X strongly attracted
    weakly attracted
    X weakly repelled
    X neither attracted nor repelled

    3. The attempt at a solution
    Well, i first figured that the negatively charged ball and the side A of the rod would weakly repel, seeing that there are two negative charges, and one postive charge, a ratio of 2:3 negative.
    -that answer was wrong
    then i thought that since it was an insulator, and is not even really charged (having a nuetral charge as a whole) it would be neither attracted nor repelled.
    -also wrong.
    -so, an insulator does not transfer charge well, but i dont see how this helps me answer the question really.

    so it's weakly attracted because the insulator rearranges to give a small dipole moment, which makes it weakly attracted?
    Last edited: Jan 27, 2009
  2. jcsd
  3. Jan 28, 2009 #2
    Right. The negative charge on the ball will attract the positive charges on the rod and repel the negative charges.

    The image of the rod is to show you that there is no overall charge on the rod.

    Have you had any lab practice using gold leaf electroscopes? Very instructive!
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