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Electric energies between 2 pt charges

  1. Apr 17, 2005 #1
    +2Q and -Q two pt charges are r apart. AS no external agent exists, they attract to each other and each gains +Q/2 after conduction. Like charges repel. At same distance at r, 2*k(2Q)(-Q)/r = 2*k(Q/2)sq /r + 2 KE...
    but what i want to know is that when is the like charges repel......just after a -Q of electrons flow from -Q to 2Q they repel...does conduction happen in a very short time to share equal charge of Q/2 before repulsion?? Or just just after a -Q of electrons flow from -Q to 2Q they repel???
  2. jcsd
  3. Apr 17, 2005 #2


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    That "conduction" is nothing but an electric charge transport process whose main purpose is to equate the electric potential.It happens till the potentials are equal.

  4. Apr 18, 2005 #3


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    As I understand what you are saying, there are two point charges separated by a distance r. Some mechanism such as a very thin wire provides a path for charge to flow from one point to the second point. The initial charge configuration has -Q at one point and +2Q at the other. A current will flow from one point to the other until there are equal charges of +Q/2 at both points.

    As long as one point is positve and the other is negative, there will be attraction. When the charge at the initially negative point is zero, there will be no attraction. As soon as the intially negative point starts accumulating net positive charge there will be repulsion. All of this neglects any charge remaining in the conducting mechanism (wire) that allows the charge to redistribute.

    It is of course a hypothetical problem, but it is very important that the charges are point charges. If the charges were distributed on the surface of sphere, for example, When one shere is neutral and the other has charge Q there would be attraction because the charge on the neutral sphere (or on the positive sphere) would not be uniformly distributed. Negative charges would be attracted to and get closer to the positive sphere, resulting in an attraction between the sheres
  5. Apr 20, 2005 #4
    No OlderDan. You misunderstood me a bit. My view is that when two point charges separated by a distance r attracts each other spontaneously. When they contact, redistribution of charges begins. Electrons flow from Point charge of -Q to Point charge of +2Q, and when it flows -Q to point charge of +2Q, they become 0 and +Q respectively. At that time, there is no attraction between the 2 new pt charges as they are not of opposite charges. Also as they at point charges of no volume or surface, no induced charges on the neutral one.
    Then, how could we said when 2 original pt charges make contact, each on then carry same charges before repulsion?
  6. Apr 20, 2005 #5
    just after state of 0 and +Q for the two charges, further flow of charges make them same kind of charge (+charge), repulsion separates them. And no more flow of charge between them happens ><
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