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Resistance and Electric Potential

  1. Mar 13, 2013 #1
    This is probably a simple concept but I'm struggling a little bit understanding it. When power is dissipated through a resistor, how is potential actually lost? I understand energy is converted into heat and other forms, but isn't potential just defined as a function inversely proportional to distance and proportional to charge (i.e. q/r)? I'm sure I'm misinterpreting the different terms, though, because potential is at approximately the same level at all points on a conductor (assuming negligible resistance), so it can't simply be a function of distance.
  2. jcsd
  3. Mar 13, 2013 #2
    Potential is a function of distance from charge, but each point in the conductor is roughly equally far apart from a similar amount of charges. This is what makes it a conductor. The charges in a conductor are free to move around. So if at one point there is higher potential than another, this will cause charges to move. They will move until they minimize their potential and at this point the potential will be uniform throughout the conductor. (the charges have naturally arranged themselves such that they are roughly equal distance from each other)
  4. Mar 13, 2013 #3
    Oh I see. That makes a lot of sense. So if there was no resistor in a circuit, would the potential just keep building up?
  5. Mar 13, 2013 #4
    The current would build up. The battery or power supply is designed to put out a constant voltage, which is potential. So the potential across your entire circuit is constant.

    For the situation with no resistor you should remember that nothing is a "perfect" conductor. The wire has a small amount of resistance. If you have no resistor in the circuit then you cant really neglect the wire's resistance, because thats all you have. With no resistor you have the minute resistance of the wire which leads to very large current (via ohm's law).
  6. Mar 13, 2013 #5
    Okay. One last thing regarding this... How does this work regarding multiple resistors, for example two in a series? That is, what causes the change in potential between the terminals of an individual resistor, when the resistors themselves do not affect the charge distribution? I understand a battery creates an emf by moving particles, but what changes the potential within a circuit?
  7. Mar 13, 2013 #6
    Good question. I think resistors do affect the charge distribution. Or I should say, in a resistor the charges are not as free to move around. Because they don't move around as easily they can put up a local electric field that "resists" the current entering the resistor. Then you have a lower potential on the other side, since the other side is connected to the battery.

    Im sure this can be explained better by someone more knowledgeable...
  8. Mar 13, 2013 #7
    Okay thank you for your help.
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