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Force of attraction between induced charges

  1. Aug 31, 2014 #1
    1. The problem statement, all variables and given/known data

    attachment.php?attachmentid=72584&stc=1&d=1409474742.png

    After induction, the cola can has +ve charges on one end and the -ve charges on the other end. Now when we touch cola can with our hand, why does electrons start flowing through it and get grounded.

    Doesn't the +ve charges on the one end of the can attract the -ve charges on the other end, and thus stop it from escaping via hand.
     

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  2. jcsd
  3. Aug 31, 2014 #2

    ehild

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    The electric field becomes zero in the metal wall at the end, so the positive and negative charges accumulated at the opposite sides do not attract each other. The negatively charged object keeps the opposite charges as near as possible on the can, while the electrons at the far end jump happily onto your finger when you touch the can.

    ehild
     
  4. Aug 31, 2014 #3
    I have googled, but could not find explanation anywhere. Can you please elaborate? Thanks.
     
  5. Aug 31, 2014 #4
    I think I get what ehild is saying.

    In other words:

    The negative charge on the balloon repulses electrons to the opposite end of the can. If you touch the right hand end of the can, the electrons "jump happily" onto your finger because the repulsion is ongoing and the electrons now have somewhere else to go! Eventually, after enough electrons leave, the remaining positive charge on the can exactly balances the negative charge on the balloon, and no electrons move.

    In yet other words:

    The electric field becomes zero at the left hand side of the can ("the metal wall at the end") before you touch the right hand side with your finger, but the electric field is not zero at the right hand side of the can. The field forces the electrons to run down your finger when you touch the can. Eventually the electric field *does* become zero at the right hand side of the can, and indeed everywhere on the can, so no electrons move any more, and grounding is complete.
     
  6. Aug 31, 2014 #5

    ehild

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    The left-hand side of the can with the balloon nearby is like a capacitor. The opposite charges attract each other, but they can not move because of the air gap between them.

    The negative charges at the far end produce electric field in the air near them. That field induces charges in your finger tip when it gets close, and the electrons can neutralize with the charge on your finger when you touch the can. Also the negative charges on the surface of the can repel each other and they leave the surface if it is possible...

    ehild
     
  7. Aug 31, 2014 #6
    If the balloon now touches the can will electrons flow into the can from the balloon? Will positive charge flow from the can to the balloon?
     
  8. Aug 31, 2014 #7

    ehild

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    Yes, electrons can flow, and they go over to the can from the balloon. The positive charge is connected to ions and they usually do not move in a metal: they sit at the sites of the crystal lattice.

    ehild
     
  9. Aug 31, 2014 #8
    Now, I have understood it very well.

    Correct me if I am wrong.

    The force of repulsion between balloon and the electrons is greater than the force of attraction between positive ions and the free electrons in the can. I deduce this from the fact that the creation of cations and free electrons is because of this force of repulsion.

    Awaiting ur response.
     
  10. Aug 31, 2014 #9

    ehild

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    The conduction electrons are free in a metal, they are not attached to any positive metal ions. So ions need not be create, they are present, in the electron "gas". The electrons distribute evenly, so the inside of the metal is neutral. The balloon just pushes the nearby electrons farther away, and it is easy, as the electrons are free. You get a net positively charged region near the balloon and net negative charge at the far end of the can.

    ehild
     
  11. Sep 4, 2014 #10
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