A circuit is the path for the flow of electricity, and like a circle, must be unbroken for it to work. Without a circuit, electricity will not flow.
For any electric appliance to work, an electrical circuit must be present. Without a circuit to link together the individual components that make up an electrical appliance, the components would be merely a collection of disparate bits. What joins all the components together into a system is a circuit.
For a circuit to exist, two conditions must be met. Firstly, there must be a complete and unbroken pathway for the electrical current to flow. The electrical current must be able to flow from the voltage source, through all the various wires, switches and components placed in its path, and back to the voltage source. The circuit is said to have continuity when this condition prevails.
The second condition that must be fulfilled is that that there be a voltage difference between two points of the circuit. This voltage difference is called potential.
The condition required to set up and maintain the flow of an electric current are therefore as follows;
1. there must be a source of e.m.f. to provide the energy which forces electrons to move in a disliked way in a specific direction; and
2. There must be a continuous external path for the electrons to flow the negative terminal to the positive terminal of the source of e.m.f.
An electric circuit is thus a completed electrical pathway, consisting not only of a conductor in which the current will flow from a negative charge back to the negative charge.
A lamp connected across a dry cell is an example of simple electrical circuits. Current flow from the (-ve) terminal of the cell, through the lamp, to the (+ve) terminal and the action of the cell is such that it provides a "regenerative" path for the flow of electrons to be maintained through the (-ve) terminal once again.
As long as this electric pathway remains unbroken at any point, it is a closed circuit; and current flows. But if the pathway be ever broken, it becomes at once an open circuit; and no current can flow.