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High voltage electric field does not stop electric motor

  1. Sep 28, 2010 #1
    I have made an attempt at understanding electric field and the effect they have on electrons by making the following test (see attached picture).

    What I did was take a 12 volt battery and connect a fan of a psu with it so the fan starts to turn by the flow of electricity, of course. I then wondered what would happen if I introduced a strong negative electric field to the wire. In theory if the electric field of the high voltage source was large enough it would stop the electrons from flowing from the negative source of the battery to the positive battery because the negative high voltage (electric field) would repel the electrons and so stop the current flowing.

    I build a simple cascade voltage multiplier and used a piece of wire from a neon sign supplier to protect the battery and wire from -10 kilovolts. The neon sign wire itself can hold 20 kV.

    I placed the wire of the cascade voltage multiplier next to the thick insulation of the neon sign wire and so create an electric field between the high voltage source and the 12 volt wire without there being a current flow.

    My assumption was the high voltage electric field would stop the current in the wire to the fan and so would stop the fan from turning. But instead the fan kept turning if nothing was wrong.

    Could someone explain to me how it is possible to have current in a wire when the current would have to be repelled by the high voltage electric field.


    Attached Files:

    Last edited: Sep 28, 2010
  2. jcsd
  3. Sep 28, 2010 #2
    There is something in electrostatics about fields inside a conductor. Remember Faraday´s cage?
    btw. - You need two electrodes or a common ground to have an electric field.
    - Voltage and field strength are not the same.
  4. Sep 29, 2010 #3
    Thanks for the reply

    Ok so correct me if I am wrong but since the high voltage electric field stops at the outermost surface of the wire (carrying the 12 volts) and the electrons continue to flow on the inside of the wire because there is no electric field inside the 12 volt wire and so the fan is still able to turn.

    In my tests I powered the cascade voltage multiplier with a variac, the cascade voltage multiplier itself has only 1 output wire or electrode (in my case negative high voltage, to repel electrons) and the other wire to complete a circuit would be ground. But in this case the second electrode is the 12 volt wire. So I assumed all voltages were relative to ground. Would it be correct to do this in this test or not.
    Last edited: Sep 29, 2010
  5. Sep 30, 2010 #4
    You´re correct enough with your explanation.
    Let me be very technical: Of course there is a (very small) electric field along the wire, otherwise there would be no current. (Electrostatics does not consider currents). An external field induces surface charges (a distribution of the existing charges) on a conductor, which cancel the field inside.
    As far as I see from your sketch, your 12V battery circuit is isolated from the HV supply, and you better leave it so. I don´t want to be impolite: the questions you ask make me doubt if you can handle high voltage safely. Maybe you continue your experiments with batteries and low voltage DC supplies; this way, if you make a mistake, the damage will be to (hopefully cheap) components, but not to yourself.
  6. Sep 30, 2010 #5
    thank you that explains it
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