Author Topic: Electrons pushed towards surface?  (Read 868 times)

0 Members and 1 Guest are viewing this topic.

Offline aussie_laser_dudeTopic starter

  • Contributor
  • Posts: 46
  • Country: au
Electrons pushed towards surface?
« on: July 10, 2022, 09:13:39 am »
Trying to understand a subtle electrodynamics problem within a long straight metal wire with a DC current.
  My understanding is that a line of moving charge produces a perpendicular electric field higher than a stationary line of charge. This perpendicular field should push charge carriers outwards to the skin of the wire and reach some equilibrium charge distribution, thus resulting in a negative skin, and positive core. Is this a known effect?
I've been pondering this for a while and remembered there's some pretty knowledgeable guys here.
Cheers
 

Online ebastler

  • Super Contributor
  • ***
  • Posts: 7375
  • Country: de
Re: Electrons pushed towards surface?
« Reply #1 on: July 10, 2022, 09:32:19 am »
My understanding is that a line of moving charge produces a perpendicular electric field

For a DC current, i.e. charge moving at a constant speed, this understanding is incorrect. The current will produce a (stationary) magnetic field around the conductor, but no additional electric field.

For AC currents, there is indeed an interplay between magnetic and electric fields, and the resulting "skin effect" in conductors is well-known: https://en.wikipedia.org/wiki/Skin_effect
 
The following users thanked this post: eugene

Offline aussie_laser_dudeTopic starter

  • Contributor
  • Posts: 46
  • Country: au
Re: Electrons pushed towards surface?
« Reply #2 on: July 10, 2022, 11:15:53 am »
Thanks for the reply, I believe the effect i'm describing is something very different from the skin effect, it works in DC and shouldn't change resistivity of the core/skin of a wire. I think i made the example too complex by using a conducting wire.

  Imagine an electron gun firing a line of continuous current in a vacuum. Is the perpendicular electric field of the charged beam stronger than a corresponding stationary beam? I believe it is, based on numerical integration of time retarded electric fields produced from a beam of moving charges. But I'm often wrong, hence there will probably be some reason why these models are wrong?
« Last Edit: July 10, 2022, 11:23:21 am by aussie_laser_dude »
 

Online ebastler

  • Super Contributor
  • ***
  • Posts: 7375
  • Country: de
Re: Electrons pushed towards surface?
« Reply #3 on: July 10, 2022, 11:22:01 am »
Imagine an electron gun firing a line of continuous current in a vacuum. Is the perpendicular electric field of the charged beam stronger than a corresponding stationary beam?

Why would there be a "perpendicular electric field of the charged beam" at all? (Besides the radial field generated by any charge, whether stationary or moving at a constant speed.)  :-//

As stated in the first paragraph of my earlier reply, charges moving at a constant speed do not generate additional electric fields. You must be mixing something up here, maybe with AC currents and the electromagnetic waves they generate, or maybe with Bremsstrahlung from accelerated (or decelerated) charges?
« Last Edit: July 10, 2022, 11:56:27 am by ebastler »
 

Offline eugene

  • Frequent Contributor
  • **
  • Posts: 497
  • Country: us
Re: Electrons pushed towards surface?
« Reply #4 on: July 10, 2022, 03:13:05 pm »
I would add to ebastler's reply that constant speed can include 0; no current. The density of electrons is uniform in a hunk of copper sitting on a bench even though the electrons are in reality zipping around in every direction all of the time. Applying a constant DC current through the hunk of copper gives the electrons a net (average) motion in some direction, but the density remains uniform.
90% of quoted statistics are fictional
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf