A force is needed to make free electrons flow in one direction.A battery or a socket provides this force and makes them flow in a path called an electric circuit.
What is an Electric Circuit?
Requirements of a Circuit
Electric Current
Power: Putting Charges to Work
Common Misconceptions Regarding Electric Circuits
In Lesson 1, the concept of electric potential difference was discussed. Electric potential is the amount of electric potential energy per unit of charge that would be possessed by a charged object if placed within an electric field at a given location. The concept of potential is a location-dependent quantity - it expresses the quantity of potential energy on a per charge basis such that it is independent on the amount of charge actually present on the object possessing the electric potential. Electric potential difference is simply the difference in electric potential between two different locations within an electric field.
To illustrate the concept of electric potential difference and the nature of an electric circuit, consider the following situation. Suppose that there are two metal plates oriented parallel to each other and each being charged with an opposite type of charge - one being positive and the other being negative. This arrangement of charged plates would create an electric field in the region between the plates that is directed away from the positive plate and towards the negative plate. A positive test charge placed between the plates would move away from the positive plate and towards the negative plate. This movement of a positive test charge from the positive plate to the negative plate would occur without the need of energy input in the form of work; it would occur naturally and thus lower the potential energy of the charge. The positive plate would be the high potential location and the negative plate would be the low potential location. There would be a difference in electric potential between the two locations.
Now suppose that the two oppositely charged plates are connected by a metal wire. What would happen? The wire serves as a sort of charge pipe through which charge can flow. Over the course of time, one could think of positive charges moving from the positive plate through the charge pipe (wire) to the negative plate. That is, positive charge would naturally move in the direction of the electric field that had been created by the arrangement of the two oppositely charged plates. As a positive charge leaves the upper plate, the plate would become less positively charged as illustrated in the animation at the right. As a positive charge reaches the negative plate, that plate would become less negatively charged. Over the course of time, the amount of positive and negative charge on the two plates would slowly diminish. Since the electric field depends upon the amount of charge present on the object creating the electric field, the electric field created by the two plates would gradually diminish in strength over the course of time. Eventually, the electric field between the plates would become so small that there would be no observable movement of charge between the two plates. The plates would ultimately lose their charge and reach the same electric potential. In the absence of an electric potential difference, there will be no charge flow.