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Electrostat doubt

  1. May 7, 2015 #1
    1. The problem statement, all variables and given/known data
    A metal ball is connected to the ground with a wire via a switch. The switch is initially closed (i.e.the ball is connected to ground) while a charge +Q is brought close to the ball (but not touching). While the charge is near the ball, the switch is opened and then the charge is taken away. The charge on the ball is now

    2. Relevant equations
    i think the ball should accquire negative charge due to induction i.e -Q but as the switch is open the charge should flow to earth.so net charge should be zero or neutral.


    3. The attempt at a solution
    solution is negative charge on ball. please help me fiqure out.
     
  2. jcsd
  3. May 7, 2015 #2

    CWatters

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    The ball is initially connected to ground by a wire. What happens to the +ve and -ve charges on the ball when a +ve charge is brought near it?

    PS: If you don't know perhaps read up about lightning and how charges on things like church spires move when a charged cloud comes near,
     
  4. May 7, 2015 #3

    Hesch

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    While the switch is closed, and a positive charge is brought close to the ball, negative charge is attracted from ground into the ball.

    Now you at first open the switch, and thus the negative charge is shut in. Then you remove the positive charge, not attracting the negative charge anymore, but the negative charge has nowhere to go and must remain in the ball.
     
  5. May 7, 2015 #4

    cnh1995

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    I think there should be a negative charge on the sphere now. When +ve charge is brought near it and it is grounded, a -ve charge would be induced on it and the +ve charge should flow into ground.. So now it has a net -ve charge in the grounded state. After disconecting it from the ground, this -ve charge should remain on it.
     
  6. May 7, 2015 #5
    thanks i finally got i
     
  7. May 7, 2015 #6

    CWatters

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    Cnh1995 & Hesch..

    Remember in the homework section of the forum we shouldn't just give people the answer - just hints so they can work out the answer themselves.
     
  8. May 7, 2015 #7

    rude man

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