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I have learnt that the electric field that is responsible for current flow is generated inside a conductor as soon as the two ends of the conductor are connected or brought in contact with the two terminals of the battery. I have also learnt about the hydraulic analogy according to which the electric field is established across the conductor in the same way as hydrostatic pressure is transmitted across a fluid.

But I'm not convinced with this analogy neither can I see any mechanism by which the electric field is established across the conductor.

I reflected that the electric field may be established by some induction, i.e. maybe the electrons in the vicinity of the electrodes are drifted towards or away from the charged electrodes and this drift of charge carriers and the subsequent development of a non - zero charge in that region induces the electrons in a farther region to respectively drift towards or away from the nearer electrode. Am I correct in my thinking?

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    $\begingroup$ Possible duplicate of How does electricity propagate in a conductor? $\endgroup$ – John Rennie Dec 6 '15 at 11:03
  • $\begingroup$ I'm simply asking if induction is the mechanism or not... And it possibly has nothing to do with quantum mechanics. $\endgroup$ – Siddharth Joshi Dec 6 '15 at 12:29
  • $\begingroup$ Please can you make the effort to explain the exact mechanism because I don't find anywhere in the answers to that question that electric field is set up by induction, nor am I getting a clear picture in my head of what they're saying $\endgroup$ – Siddharth Joshi Dec 6 '15 at 12:34
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First of all it is not instantaneous, all electric/magnetic impulses are limited by the velocity of light.

On a simple picture, as you find the answers in the link confusing, concentrate on the neutrality of each molecule in the wire before an electric field is imposed by the battery. There are electrons on the outside of the molecule and protons inside so the total field outside a molecule is for our purposes zero. A field from the battery terminal attracts an electron at a time delta(t) and imposes a velocity of attraction. Suddenly that molecule acquires an electric field, a positive one, which will pull an electron from an adjacent molecule and the electric field appears further down, and so on down the line to the other terminal of the battery. This happens very fast, because even though the electron moves fairly slowly with a drift velocity, the signal travels fast and part of the signal is the electric field that appears much faster than the electron drift velocity. Think of a stadium wave where the wave moves but the people stay in place, happening very fast as far as electrons are concerned.

This is a gross explanation, because in metals once a field starts the electrons move in bands not attached to individual atoms, thus have higher mobility than in non conductors, but that is a story you will learn if you study physics further.

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The battery already has electric field around its poles. When you connect wires to the battery, charges redistribute along the surface of the conductors in the circuit. These surface charges, including those on the battery, maintain the electric field inside the conductors and thus cause electric current.

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  • $\begingroup$ Why should the conductor have net charges on the surface. Why couldn't there be net charges on the inside of conductor as well? $\endgroup$ – Siddharth Joshi Dec 6 '15 at 15:48
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    $\begingroup$ @SiddharthJoshi, there could be some net charge inside the conductor if the current was not stationary, but generally its constituent particles will repel each other and will tend to settle on the surface just as in electrostatic situation. In stationary current situation, no net charge is present inside the conductor. $\endgroup$ – Ján Lalinský Dec 6 '15 at 20:21

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