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Electricity & charge

  1. Jul 24, 2017 #1
    1. The problem statement, all variables and given/known data

    Screen Shot 2017-07-24 at 6.49.06 pm.png
    2. Relevant equations

    3. The attempt at a solution
    I chose B because I thought the positive charges in the insulator would attract the negative charges in the conductor to one side. I do realise that it is earthed for a short time. What difference does it make?

    Thank you
  2. jcsd
  3. Jul 24, 2017 #2
    What happens when "the insulator is removed"?
  4. Jul 24, 2017 #3
    The negative charges redistribute themselves evenly around the conductor?
  5. Jul 24, 2017 #4
  6. Jul 24, 2017 #5
    Oh~so 'earthing' has the same effect as removing the insulator?
  7. Jul 24, 2017 #6
    No. Earthing allowes the (previously isolated) conductor to acquire a negative charge as a result of attraction from the positively charged insulator. Then the earth is disconnected (the question doesn't say this explicitly, but it is implied in "earthed for a short time") and then the insulator is removed, and the negative charge is redistributed.
  8. Jul 24, 2017 #7
    okay, so if the insulator was not removed, the answer would have been B?
  9. Jul 24, 2017 #8
  10. Jul 24, 2017 #9
    Thank you so much!
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