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I know that to have a current in a circuit we need a potential difference that creates a gradient that makes electrons move from low potential to high potential. My question is that how, in a circuit, potential difference makes the charges move so perfect ( along the wire because that would need a constantly changing force on the charges along the wire) Thanks

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  • $\begingroup$ Electric field which provides the drift velocity and hence electrons drift or say pushes each other and hence appear to be doing slow motion.en.m.wikipedia.org/wiki/Drift_velocity Maybe this could provide some insights. $\endgroup$ May 4, 2018 at 11:57
  • $\begingroup$ Ok but how does the electric field point in the direction we need it to ie. perfectly along the wire $\endgroup$
    – user194517
    May 4, 2018 at 12:10
  • $\begingroup$ see for that you should know the direction of electric field which is from positive to negative or say high potential to low potential. $\endgroup$ May 4, 2018 at 12:12
  • $\begingroup$ If I made a circuit with alot of loops then how would the electric field manage to point along the loop $\endgroup$
    – user194517
    May 4, 2018 at 12:24

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Think of the battery as having plenty electrons stuffed together at its terminal (its internal electromotive force carries them there). They all repel and want to move away. They can't, since the surrounding air is non-conductive. The resistance in an insulating material is much stronger than the repulsion force.

Then you attach a wire. They now move because there is a path with much less resistance than the repulsion force. When an electron has moved away from the terminal, we might think they it slows down since the repulsion reduces with distance. Indeed, yes, but the electron is not alone. Behind it is the next electron, pushing forward. They all queue up behind one another and move at the same pace.

Now bend the wire. An electron moving forward due to it being pushed from behind, now cannot continue moving forward. The insulating material outside the wire resists it more strongly than it is being pushed. So it must take another path. And there is only one other path along which the resistance is small enough - that is to continue along the wire.

Was there no available path, then it had to stop. Then it would stay where it is and start repelling lyver electrons from arriving. It's own repulsion force is still small compared to the combined push starting from the battery, so more electrons will arrive. This gradually increases the repulsion which in turn gradually reduces the current. Soon that repulsion balances out the battery push, and everything stops moving.

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Two points here. First, you would need quite a strong force to make an electron escape the wire. It would usually be a lot easier for the electron to follow the wire. Second, in a steady state, the electric field is perpendicular to the wire. If a voltage is applied to a bent conductor, surface charges accumulate in curved parts which leads to a net electric field in axial direction.

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  • $\begingroup$ I know my question would sound silly but can you also tell why electric field in a wire is perpendicular to the wire $\endgroup$
    – user194517
    May 4, 2018 at 12:50
  • $\begingroup$ This is actually a consequence of the electric charges accumulating on the wire surfaces. If the electric field is not perpendicular to the wire, it will force charges to reorganize in such a way that the field is perpendicular to the wire again. $\endgroup$
    – lmr
    May 4, 2018 at 12:54

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