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What charges on high voltage circuits?

  1. Oct 31, 2011 #1
    People usually use an electrostatic voltmeter for direct measurement.
    I would like to know what kind of charges is on following high voltage circuits.
    Will it be positive or negative charges?
    Does anyone have any suggestions?
    Thanks in advance for any suggestions

    high-voltage-measuring-techniques-800x800.jpg
     
  2. jcsd
  3. Oct 31, 2011 #2

    Matterwave

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    Charges which flow (current) are always the negative charges. The electrons move, the protons in the nucleus don't really move.

    The current, though, is defined as the movement of positive charges in the other direction. This is due to a bad convention that historically people used.
     
  4. Oct 31, 2011 #3
    Does it apply AC here? so the charges will change alternatively, so electron and proton does not move a far distance.

    If there is a massive negative charges moving along the cable, does it generate any magnetic field? which distorts the north within the compass.
    Does anyone have any suggestions?
    Thanks you very much for any suggestions
     
  5. Oct 31, 2011 #4

    nsaspook

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  6. Oct 31, 2011 #5

    Matterwave

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    Always (in a wire anyways), the neucleus doesn't move much. For AC current, it's the electrons that move in alternating directions. A magnetic field is produced, and it is produced even in the constant DC current case.
     
  7. Nov 1, 2011 #6
    So does compass not work very well near the high voltage cable? right?
    Thanks everyone very much for any suggestions
     
  8. Nov 1, 2011 #7
    I've never noticed any influence on a compass when walking under high voltage cable.
    I think the needle can't react fast enough to move with the 50 or 60 Hz oscillations of the magnetic field, and the average field will be zero with AC.

    Of course, a magnetic field is produced by a high current, so the magnetic field isn't all that big, because the current might be only 1000 A or so, you can't get close to it, and there will be wires with currents in the opposite direction that will cancel out most of the field.
     
  9. Nov 1, 2011 #8
    What do you mean by "Charge on the circuit"? Virtually, there is no net charge on the circuit or hardly any since wires are highly conductive. Actually, it is a flow of electrons, which carry negative charge, but whenever you take a section of the wire there is no net charge, although electrons are moving.
     
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