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Voltage and current

  1. Jun 4, 2014 #1
    In an eletric circuit, can exist nonzero voltage and zero current? Can exist zero voltage and nonzero current?

    What the voltage make (in the sense of task/function/operation) in the circuit?
    What the current make (in the sense of task/function/operation) in the circuit?
     
  2. jcsd
  3. Jun 4, 2014 #2

    Matterwave

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    1. You can have non-zero voltage and zero current if there is insulating material (e.g. air) between the two points. This is the case, for example, on a Van de Graaff generator which has a high voltage due to static electricity (non moving electricity = no current).

    2. If you have no voltage across a circuit element, then you don't have anything to drive a current. Conventionally speaking, from an electrical engineering standpoint, the answer is probably no. However, you can have charges (say free-floating charges) freely moving in a direction which would then be called a current. For example, in a cathode ray tube, you accelerate the charges over a short distance (using a voltage) and then they basically free-stream to the other side of the tube. During it's free-stream period, there's no voltage difference, but there's a current.

    Voltage is the potential energy (per unit charge) stored between a configuration of charges. This potential energy is what can accelerate charges from one place to another.

    Current is just the movement of charges (how much charge passes a point in space per unit time).
     
  4. Jun 4, 2014 #3
    Good explanation! :D
     
  5. Jun 5, 2014 #4
    Superconductors have non-zero current w/ zero voltage. Either one can exist w/o the other under static conditions (not varying w/ time). Under dynamic conditions, you can't have one w/o the other. BTW, voltage is not what "drives current". A power source which translates energy from one form to another is what makes this happen, i.e. battery, generator, etc.

    Claude
     
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