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Charges and insulators

  1. Jun 23, 2014 #1
    First question i have is about the common glass rod-cloth experiment where the one gets plus charged and the other minus charged.The plus charged item how does it get back the electrons that it missed?If we touch it again with the other one or even through the air?And the minus charged how does it release its additional electrons?

    Secondary i want to ask something about insulators.I know that if we apply a potential difference through an insulator its electrons have strong bonds with each nucleus so we have few free electrons and so it is a non conductor.If we put an insulator though in the middle of a circuit,for example a plastic item that has a metal wire connected to its one end and another wire to its other end and both wires are connected to a battery,then few of insulators electrons will move but will wire's electrons run through the insulator?If yes or not please explain the reason.

    Thanks in advance
  2. jcsd
  3. Jun 23, 2014 #2
    Yes if we touch the items for a brief period of time (without rubbing them against each other) the additional electrons will get attracted by the positive ions and both items will return to neutral charge.
    In general if we bring the charged item in contact with any other item charged or not (which is not a perfect insulator) there will be moving of electrons between the two items (from the item with the lower potential to the item with the higher potential), until both items are in same potential (or until the free electrons in the item with the lower potential have been exhausted, that is the case where the item is bad conductor and there is really big potential difference between the two items).
    Ofcourse you might ask me here what is potential and potential difference. This would be hard to answer without getting into mathematic details. Potential depends not only on the amount of charge one item has but also how this charge is distributed inside or at the surface of the item. We can say that the item which is more negatively charged is in lower potential however this is not always the case.
    Well what you actually do is forming a circuit in series with the battery the insulator and the wires. In a circuit in series , the current is everywhere the same. Because of that and because the current in insulator will be small, the current at the contacts between the wires and the insulator will also be equal small, so very few electrons from the wire will move through the insulator and from the insulator through the other wire.

    Last edited: Jun 23, 2014
  4. Jun 24, 2014 #3
    Okay thanks.In the first question though,if we don't just touch the differently charged items to restore the balance how will they become neutral again?Through the air?
  5. Jun 24, 2014 #4
    If the charge in the item is small (and it is small in the rod-cloth experiment), it can become neutral by getting opposite charges through the air. Air is a very good insulator though so (similar to your 2nd question) there would be very few electrons or even positive ions flowing through air.
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