Electric current is defined as the rate of flow of electric charge through a conductor. If a charge Q flows through a cross-section of a conductor in time t, the current I is given by I = Q/t. Current electricity, unlike static electricity, involves a continuous and sustained flow of charge, which is what powers all electrical appliances and devices.

Unit: The SI unit of electric current is the ampere (A), named after the French physicist André-Marie Ampère, often called the father of electrodynamics. One ampere is defined as a flow of one coulomb of charge per second (1 A = 1 C/s). Current is measured using an instrument called an ammeter, which is always connected in series in a circuit.

Conventional Current vs. Electron Flow

This distinction is one of the most commonly tested conceptual points in this chapter. Well before the electron was discovered, scientists had already established a convention for the direction of current flow: conventional current is taken to flow in the direction in which positive charge would move, that is, from the positive terminal of a source, through the external circuit, to the negative terminal. However, in metallic conductors, it is actually the negatively charged electrons that physically move, and they move in the opposite direction — from the negative terminal to the positive terminal through the external circuit. In other words, the direction of conventional current is exactly opposite to the direction of actual electron flow in a metallic wire. This convention, though it does not match the physical reality of electron motion, is retained throughout physics and electrical engineering because changing it at this stage would require rewriting virtually every textbook and circuit diagram in existence, and because for most circuit calculations the choice of direction does not affect the outcome.