Sources of Electric Field inside a conducting wire.

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  • #1
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Main Question or Discussion Point

Suppose that we have a wire that connects the two poles of a DC battery. The current produced indicates the presence of some Electric Field within the wire, having a constant magnitude and a direction that follows its path.

Now the question is : What is the source of that Electric Field?

The way I see it, it can’t be the charges that accumulate in the poles of the battery, for if that was true, the Electric Field would resemble the field of a dipole, diminishing at higher distances (but the wire could extend hundreds of meters away from the battery).

So is it the moving charges themselves that produce the Electric Field within the wire?

If that’s the case, could someone give me a qualitative description of how such a field develops?

Moreover, how could it be that the same sources (usually electrons) produce no Electric Field outside the wire?

Any help much appreciated.
 

Answers and Replies

  • #2
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It is the charges in the poles. The dipole field you mentioned exists locally at the terminals then travels out a bit lower than the speed of light until it hits the end of the loop whereupon it is reflected. By radiation (and absorption in the internal resistance in the battery and ohmic losses in the wire) this dipole disturbance dies out leaving behind the steady voltage drop you expect along the wire. This steady voltage is sustained in each segment of wire by the fields in the adjacent segments.

There will be an electric field outside the wire, tangential to the wire if the resistance is not zero.
 
  • #3
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Thank you for your reply, but that was somehow confusing to me! Especially this part (the current is steady) :
There will be an electric field outside the wire, tangential to the wire if the resistance is not zero.

I’m really interested in how the Electric Field inside a conducting wire is produced. It shows some very interesting features (steady magnitude, always tangential to the wire, no field outside of it). I can’t yet understand how this can happen in a segment near the battery and still in another one say a hundred meters away. What's the source of such Field?

All I can think is that the Field is somehow produced by the electrons set in motion within the wire, pushing one another, in a way that reminds the motion of a liquid in a pipe.

If that is true then basic notions of EM, such as charge and Coulomb’s law should suffice to describe the mechanism.

Anyone could help me conceptualize this?
Thanks in advance.
 

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