Electric current is the flow of electric charge, and its unit is the ampere (A). The letter symbols for current are A or I, often represented by the symbol “I” enclosed in a circle. The smallest charge is carried by electrons, but in practical circuits, the vast number of electrons makes individual considerations impractical. Instead, the current flow is treated as a continuous stream of charges.
A steady current is a continuous flow of charges past an area, with 1 ampere defined as 1 coulomb of charge passing by in 1 second (Q = t = A). Despite electrons being negatively charged, the conventional current direction is considered as positive charges flowing, a historical convention that persists. The positive terminal of a battery is considered the source of current, even though electrons move in the opposite direction.
Significance of Conductors
While current does not typically flow in air, it readily flows in conductors like copper or iron. Conductors attached to a battery acquire charges on their surfaces, seeking a path from the anode to the cathode. Establishing a direct conducting path between the cathode and anode, however, results in a short circuit, destroying the battery by draining its charge rapidly.
Different units of current are used for convenience. The milliampere (mA) and microampere (µA) are smaller units, with 1 A being a relatively small unit in the power industry but a significant one in electronic circuits. The significance of current units becomes apparent in the practical applications of batteries, where a car battery might supply 1 A for 60 hours, while a flashlight battery might deliver 100 mA for 10 hours. Understanding these concepts is crucial for designing and using electrical circuits effectively.