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    An insulated metal conductor is earthed before a negatively charged object is brought near to it.
    a) Explain why the free electrons in the conductor move as far away from the charged object as they can.
    b) The conductor is then briefly earthed. The charged object is then removed from the vicinity of the conductor. Explain why the conductor is left with an overall positive charge.
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    This won't be a mark scheme answer but comes from own intuition

    a) Similar charges repel

    b) The electrons have been repelled into earth. There are now more protons than electrons in the conductor, which makes it positively charged.
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    (Original post by s.xw)
    This won't be a mark scheme answer but comes from own intuition

    a) Similar charges repel

    b) The electrons have been repelled into earth. There are now more protons than electrons in the conductor, which makes it positively charged.
    Could you explain how you came up with that answer for b in detail. Do electrons first flow from the charged object to the metal so it has a negative charge? And then when earthed the electrons flow to the ground?
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    The way I read it, the charged object is brought near the conductor, but does not touch it. This means that unless there is a spark, the electrons in the negatively charged object do not move.

    Part B is connected to Part A, which gives you a clue. It tells you that electrons in the metal conductor want to move as far as way from the charged object as it possibly can. When the conductor is earthed (briefly) the electrons seize the opportunity to move away into the earth (excuse this unscientific terminology).

    Are you familiar with the concept of earthing?

    Because the conductor was only earthed briefly (key word), when the charged object was removed, electrons were not able to return to the conductor to restore the neutral charge. Hence, it is left with a positive charge.
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