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Homework Help: Can someone tell me if conduction is more powerful than induction?

  1. Jan 22, 2014 #1
    1. The problem statement, all variables and given/known data
    In the lab I am writing about, here were the directions
    7. Predictions: Touch a metal sphere to neutralize it. Holding the plastic handle, bring the metal sphere in contact with the charged foam slab. Do not touch the sphere at any time. Take the sphere away from the foam. Has it acquired a charge? Will it shock you if touched? If it has acquired a charge, predict the polarity. Sketch and briefly explain your predictions, then check to see if you were right.

    8. Try something different: When the sphere is neutral, bring it into contact with the foam, and touch the sphere while it is touching the foam. What happened? Now take the metal sphere away from the foam. Touch the sphere again.
    9. Neutralize a metal sphere by having a lab partner touch it. Bring it close to but not touching the charged foam. Touch the sphere, then carry it several feet away. What happens when you touch it?

    2. Relevant equations

    3. The attempt at a solution
    7. -OPTION 1: Predictions: The negative charge of the foam will be transferred to the sphere due to conduction. The sphere will shock when touched because it will transfer the negative charge to the finger.

    The sphere acquired a charge which we proved was negative... It also shocked when touched. Our predictions proved correct.

    -OPTION 2: Or did we do this incorrectly? Were we not supposed to feel a shock? If so, why not? Because the foam is not a conductor but an insulator?

    8. When we touched the sphere while it was in contact with the negatively charged foam, it delivered a powerful shock.
    When we touched the sphere afterwards, it also shocked, but not as strongly.
    Both were much stronger than the shock delivered from induction. (IS THIS AN ACCURATE STATEMENT?)

    -Option 1: This was because the sphere had an overall negative charge through induction both times we were shocked.

    -Option 2: The sphere became polarized by contact with the foam. Because we touched the side of the sphere opposite the foam, we received a negative charge in the form of a shock, which gave the sphere an overall positive polarity. So, when we touch it again and are shocked, it is because we are transferring electrons to it, not the other way around.

    9. There was a shock while it is close to the foam and while it is several feet away, though the shocks were not as powerful as the ones in number 8, when the charge was conducted and not inducted. FROM THIS CAN WE CONCLUDE/BEGIN TO THINK THAT CONDUCTION IS MORE POWERFUL THAN INDUCTION?

    -For options see number 8
    Last edited by a moderator: Jan 22, 2014
  2. jcsd
  3. Jan 22, 2014 #2


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    Homework Helper

    in #9, the metal ball was not supposed to contact the negative foam; electrons were chased from the ball by the foam's Electric field, so they fled thru your body into the ground (the shock). The ball was left with way too few electrons, so it would pull some from you later if it got a chance.

    Which process has the ball closer to the source charge - contact charging, or induced charging?
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