For most practical applications, it is necessary that current flow continues for as long as it is required; this will not unless the following conditions are fulfilled:

1. There must be a complete path around which the electrons may move. If the electrons cannot return to the point of starting, then eventually they will all congregate together and the flow will cease.

2. There must be a driving influence to cause the continuous flow. This influence is provided by source which causes the current to leave at a high potential and to move round the circuit until it returns to the source at a low potential.

The driving influence is termed as the electromotive force, hereafter called the e.m.f

The direction of an electric current is by convention the direction in which a positive charge would move. Thus, the current in the external circuit is directed away from the positive terminal and toward the negative terminal of the battery. Electrons would actually move through the wires in the opposite direction.