Current in a circuit 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
 A: 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. 
A: 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.
