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As alternating current passes along a wire:

  • Different charges are pushed to the surface in response to the current charges and form an excess electric field, leaving the interior wire neutral.

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Questions:

  1. Is this view correct?
  • This would mean there are two groups of charges.
  • Experimentally: Is there a strong electric field associated with each half wave even with a low resistance wire?
  1. Does the electric field travel down the wire near the speed of light and, before a current starts, all the positive and negative half waves are established along the length of the wire. The current charges between half waves can then neutralize each other. All the half waves progressively change together near the speed of light as the alternating electric field refreshes. Charges do not form on the surface in response to current charges.
  • This can mean there is not an electric field associated with each half wave. There can still be an electric field from resistance in the wire deflecting current charges to the surface.
MarkJanus1
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1 Answers1

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From Gauss' law we get the fact that there is no field inside a closed conductor. this puts the unbalanced charges on the surface of the wire in response to the local charge-imbalance on that wire.

In large conductors the skin effect puts most of the alternating current near the surface of the wire, but that's a magnetic effect.

As alternating current passes along a wire:

A wire long enough to present even a half wave of AC is not a mere wire anymore, it's now a transmission line, and new emergant behaviours come from the wave properties of signals in wires.

Is this view correct?

The picture is a nonsense. but see Gauss' law.

This would mean there are two groups of charges.

Not really, it's all one pool of conduction band electrons, if only the surface electrons carried the charge then the bulk of the wire would not conduct current. as the potential in the wire increases caused by current flowing in the bulk of the wire charges are pushed to the surface of the wire

the distance traveled by most charges in a wire carrying domestic AC is just a fraction of a millimeter before the current reverses, in an antenna carrying radio frequency it's even less.

Also note that potential and current need not be synchronised.

Experimentally: Is there a strong electric field associated with each half wave even with a low resistance wire?

A strong external field? Yes, that's how non-contact voltage detectors work. also electrostatic loudspeakers etc. Internally, no, See Gauss's law.

Jasen Слава Україні
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  • "From Gauss' law we get the fact that there is no field inside a closed conductor". How do you explain then the electric field inside any conductor carrying a current? Because *there is* an electric field inside the conductors: E = j/sigma, directed along the conductor's path. – Sredni Vashtar Dec 31 '20 at 01:00
  • In DC, surface charges occur in response to resistance. The surface charges follow a gradient or capacitive arrangement on the surface and distribute electric fields locally in the wire to make a constant current and use all the voltage from the voltage source. Stating the wire becomes neutral when charges are pushed to the surface is an error in my explanation. Surface charges have a direct effect on the current charges. – MarkJanus1 Dec 31 '20 at 01:54
  • How that works in AC is my question. If there is a strong external electric field in AC that does not depend on resistance then in a transmission line how does that have an effect on current? Do the two half waves act as open face capacitors moving along the line and the temporary surface charges are providing the electric field locally to drive the current back and forth as the wave proceeds far from the AC source? Such an explanation would have enough surface charges for the voltage. The current would depend on the resistance. – MarkJanus1 Dec 31 '20 at 01:54