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The direction of the induced electric field

Physics Asked on March 11, 2021

enter image description hereRecently I got stuck witht the following problem.

Imagine we have uniform a magnetic field which induction points upwards. The fields strength is steadily decreasing. If we put an iron coil perpendicular to the magnetic induction vector, then, obviously, there will be electric current induced in the coil.

However, as I understand, the coil itself is only a ‘marker’ that displays the electric field lines that actually make the electrons move. It means that the elcetric field is there even when there is no coil.
Now the problem:
I can imagine some coils being close to each other. It will essentially mean, that it in one of them the current will go one way and in the other – the opposite. How can this possibly be?

I looked at this answer as it is phrased very close to what I want and still I couldn’t get the idea. Could the answer be presented in more layman terms .

2 Answers

Given your drawing, equal area loops normal to a uniform, changing field, all we can say is this:

1)The integral around the loops of the electric field dotted into the line element are equal--it says nothing about the direction of the field at any point.

2) (Lenz's law) The direction the current flows is the direction that "keeps the magnetic field going"--in layman's terms.

That current flows in opposite directions where the loops are in the same physical space does not contradict point 1, nor point 2.

Answered by JEB on March 11, 2021

I think what is missing in the analysis is the charge carriers that carry the current (i.e. the electrons). Electric field would be indeed there, if there is no coil, but without coil there are no charges that could be affected by this field and consequently there is no current. If the two coils in the image are joined together, there will be indeed no current through the central part.

Answered by Vadim on March 11, 2021

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