# The Naked Scientists Forum

### Author Topic: Can DC voltage move through air ?  (Read 580 times)

#### Weirdodo

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##### Can DC voltage move through air ?
« on: 07/07/2016 14:25:34 »
The other day i was fooling around with my multimeter and when i approached one of the nodes to the extremity of a wire carrying 1000 V DC
I found some voltage on the voltmeters screen. It varied from 10 millivolts to 70 volts depending on how close the node was to the wire. Thr closer it was the higher was the voltage . And when the voltmeter touched the wire the new number got to 1000 V which was pretty obvious. The question was,
Did the voltage move through the air and reached the electrode ? If not, then what caused the voltage reading on the voltmeter ? Thank you very much.

#### Colin2B

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##### Re: Can DC voltage move through air ?
« Reply #1 on: 07/07/2016 14:41:33 »
Voltages as high as this can ionise the air forming a conductive region that allows charge to flow. If you had used an earthed wire rather than your meter probe (not recommend by the way) you would have drawn a spark from the 1000v line before the 2 wires made contact.

If you want to learn more look up something like electric corona, corona discharge.

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#### evan_au

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##### Re: Can DC voltage move through air ?
« Reply #2 on: 07/07/2016 19:24:11 »
Quote from: Weirdodo
on the voltmeters screen. It varied from 10 millivolts to 70 volts
An electronic digital volt meter often has an impedance of about 10 MOhms.
Small currents through the air could register as a voltage on such an instrument.
I expect they would not register on an old-fashioned moving-coil analogue meter, which has a much lower impedance.

#### syhprum

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##### Re: Can DC voltage move through air ?
« Reply #3 on: 07/07/2016 19:37:55 »
There is an electrostatic field between the HV line and ground, when you move into that field a voltage is induced into your meter leads, this is a purely  capacitive effect that would work in a vacuum and does not depend on any ionisation.

#### chiralSPO

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##### Re: Can DC voltage move through air ?
« Reply #4 on: 07/07/2016 20:14:26 »
What do you mean by "a wire carrying 1000 V DC"? voltage is a difference between two potentials, so you always have to specify what the voltage is compared with. Was the wire at 1 kV vs ground? Was the wire before a load where the potential fell off by 1 kV? Was the wire connected to a series of batteries such that the electromotive force was 1 kV? etc. etc.

If there was substantial current going through the wire there may have been an magnetic field around the wire that could potentially generate voltage readings in a multimeter. If there was a strong electric field around the wire, it could be that if one of the leads to the multimeter was closer to the wire than the other one, they could sense the difference in potential (if we assume each of the leads is 20 cm, and they are extended away from each other, then the 70 V reading would correspond to about 70 V / 0.4 m or 175 V/m, which is much less than the 3x106 V/m needed for arcing...)

EDIT: I see I crossed posts with syphrum...

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##### Re: Can DC voltage move through air ?
« Reply #4 on: 07/07/2016 20:14:26 »