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I know that moving charges produce both magnetic and electric fields. The image given below is of electromagnetic field. I was able to identify the magnetic field. But,I do not know where the electric field is? enter image description here

Qmechanic
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CandidFlakes
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  • This is a wire through which flows an electrical current, think about it. Does such a wire have an electric charge? –  Jun 17 '17 at 13:14
  • Yes its true that a moving charge produces electric field as well, but for a steady current you have as many positive charges in a given place to negative charges, so the total charge density remains zero. Basically there is no pile up of charges. And I guess you are calculating $\textbf{B}$for steady currents. So no question of $\textbf{E}$. – sbp Jun 17 '17 at 13:27
  • @LucJ.Bourhis, good point but limited to the case that the current is constant with time. If the current is time varying, there is an induced electric field as well as an electric field due to charge separation. – Alfred Centauri Jun 17 '17 at 13:29
  • Then,where is such electric field located? Is it around the wire or inside the wire?if possible, please give a diagram. – CandidFlakes Jun 17 '17 at 13:41
  • @AlfredCentauri Yes, good point too of course. I should have made it clear I only considered a steady current indeed. Which is really what this schematics seem to suggest, as otherwise the direction of the magnetic lines would change with time and it would not make much sense. –  Jun 17 '17 at 14:01
  • The electric field is zero. So it is nowhere to be seen. –  Jun 17 '17 at 14:01
  • I don't get @sbp's comment. Surely there is an electric field within the wire? Because there has to be a potential source (eg battery) for a current in a wire with resistance. Unless this question is assuming an ideal wire. – Zhengqun Koo Jun 17 '17 at 14:13
  • @LucJ.Bourhis But can you please tell me an example of a condition where moving charges produce both electric and magnetic fields ?If,possible please give a labelled diagram – CandidFlakes Jun 17 '17 at 14:14
  • Can someone please locate the electric field formed at atomic level in the mentioned diagram? – CandidFlakes Jun 17 '17 at 14:16
  • @KooZhengqun yes,your thoughts are correct. I am also trying to ask the same thing.....can you answer please? – CandidFlakes Jun 17 '17 at 14:18
  • @NavneetKumar Accelerating charges produce electromagnetic waves, which are propogating electric and magnetic waves. Example: Radio transmitter / receiver. – Zhengqun Koo Jun 17 '17 at 14:21
  • As @KooZhengqun said, a beam of electrons that would be deflected by a static magnetic field, would radiate electromagnetic waves, i.e. create the both of an electric and a magnetic field. But the electric field would be nothing like just the electrostatic field of a charge at rest. But that's a completely different question now… –  Jun 17 '17 at 14:28
  • Reading through the comments, it's clear that your question is unclear. – Alfred Centauri Jun 17 '17 at 14:33
  • I'd say we reached an understanding –  Jun 17 '17 at 14:43

2 Answers2

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First let's assume DC. The electrical wire is neutral: as many negative electrons as positive atomic nuclei in any part of the wire. Thus there is no electrostatic field outside of the wire and the lines represent the magnetic field lines. However for the electrons to move through the wire, there needs to be an electric field. This field is localised inside the wire, and it is on average always along the direction of the wire, thus winding up as the solenoid winds up. This field strength is also constant, and with a good approximation, uniform along the wire.

Now if the current was AC, the magnetic field would vary with time, its strength at any point passing through a maximum, then declining to zero, changing direction and reaching a maximum in the other direction, to then decline again, etc. A changing magnetic field creates a changing electric field according the Maxwell equations which rules electromagnetic phenomena (i.e. electric + magnetic + their interplay). So in this case, there would be an electric field outside the wires. I don't know what it would look like for the exact situation of your diagram, except in the central zone of the solenoid where the magnetic field is nearly uniform, and its direction along the axis of the solenoid: in that zone, the electrical field induced by the varying magnetic field would be radial. I am sure you can draw a diagram yourself!

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This lecture gives a good overview of this. http://faculty.uml.edu/Andriy_Danylov/Teaching/documents/L18Ch33InducedEcovered.pdf (Pg: 11-12)

Lenz's law provides a lot of insight into this question. An AC solenoid will induce a changing magnetic field. This changing magnetic field acts to impede the current direction in the solenoid, so from here, you can likely already see that the electric field is made in the direction that opposes the electric field in the wire driving the current.

Alpha Delta
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Potatoconomy
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