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Homework Help: Negative rod to uncharged metal ball:

  1. Jan 26, 2008 #1
    [SOLVED] negative rod to uncharged metal ball:

    1. The problem statement, all variables and given/known data
    If a negatively charged rod is held near an uncharged metal ball, the metal ball:
    1. becomes positively charged.
    2. becomes polar.
    3. Effect cannot be determined.
    4. becomes negatively charged.
    5. is unaffected.

    3. The attempt at a solution
    I guessed number 4, thinking that if the negative rod touched the neutral ball, the ball would gain electrons ( since its easier to gain and lose electrons - very very difficult and rare for an object to lose or gain protons )

    This would make the ball negative but I was wrong... whats the catch here?
  2. jcsd
  3. Jan 26, 2008 #2
    The negative rod does not touch the ball though. What do you know about the electric field inside of a conductor?
  4. Jan 26, 2008 #3
    oh my god. i read it as touched.

  5. Jan 26, 2008 #4
    there is no change - no contact was ever made.
  6. Jan 26, 2008 #5
    wait, unaffected is the wrong answer x_x now what am i missing?

    wow - yikes... is it not determinable?
  7. Jan 26, 2008 #6
    The answer is it becomes polarized ; the ball has an effective separation of charge
  8. Jan 26, 2008 #7
    Yes you could get the answer by knowing that inside the conductor that the electric field must be zero. So when the negative rod goes towards the conductor, then a bunch of positive charges need to go towards the end the rod approaches, and then negative charges must accumulate on the other side. It polarizes.
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