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Simple electric field concept

  1. Jun 13, 2003 #1
    If an electric field is due to 2 parallel plate conductors carrying equal and opposite charges, which plate got the higher potential, positive one or negative one?

    Electric potential = Q/(4*pi*ε*r)

    If charge, Q is negative, electric potential is negative, does it mean that the negative plate has a lower potential than the positive one?

    However in a battery, say a dry cell, negative terminal has higher potential then the positive one. Hm... I'm a little bit confused.
  2. jcsd
  3. Jun 13, 2003 #2
    The positive plate is the plate of higher potential. If you let an electron in the middle of the two plates it will be accelerated to the positive plate
    In a battery, the positive pole has the higher potential. In a circuit, the electrons go out of the negative pole, travel the circuit, and return to the positive pole. Is current in the drawings to represent that the electrons flow from positive pole to negative pole, but this sense for the current, named "conventional current", it's not the real. It's made this way for historical reasons, but i think that conventional current should be eliminated
  4. Jun 13, 2003 #3


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    In some sense I agree that 'conventional current' is a rather bad historical hold-out, except that really, it's just a convention. It's no worse that the right-hand rule, or any of the other conventions in physics.

    The physics of most of the electronics world doesn't change if you use positive charges moving in one direction, or negative charges moving in the other direction. For example, a wire carrying positive charges in one direction and a wire carrying negative charges in the other direction will produce identical magnetic fields. Since both of these currents result in the same phenomena, it makes sense to refer to them both as being the "same" current. The direction chosen to represent that current happens to correspond to the direction positive charges would move. Sure, the charge carriers in most electronics are actually negative -- but in semiconductors, the charge carriers can just as easily be positive.

    - Warren
  5. Jun 14, 2003 #4
    Thanks for your replies.

    so does it mean electrons move from lower potential region to higher potential region in an E field while a positive charge moves from higher potential area to lower potential area ? And field lines are drawn from higher potential region to lower potential region, right?

    If a postive charge is placed in an E-field, it moves from higher potential region to lower potential region, loss in pe becomes gain in ke, that makes sense to me.

    Ok, if an electron is placed in an E-field, it gains electronic potential energy by moving from lower potential region to higher potential region. At the same time, it accelerates to the higher potential region and thus gain in ke also. Where does the gain in energy come from?

    I've heard of it too. I'm imagining large positive charge carriers move to one side while small electrons just stay still. Kinda interesting though perhaps that's a false imagination. :smile:
  6. Jun 14, 2003 #5
    What charges (possitive or negative) want to do is rise to zero potential difference in the system, or equalization.

    Imagine an sphere with electrons. It is at a lower potential (-V) due to their charge and inner repulsion. The electrons will go to infinity, to a higher potential (0V), but from the point of view of the electrons, it is in fact a "lower" potential.

    The charges increment or decrement their inner PE, but in order to equalyze or reduce the total potential difference in the system.

    When an an electron moves from lower PE to higher PE, it's just annuling some PE difference that existed.

    But your question is still interesting, and i hope someone could explain it in a better way.
  7. Jun 15, 2003 #6


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    Why do you post in this thread? You have no idea what you're talking about.

    - Warren
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