Electric current is just the rate at which charge flows through a wire: measured in amperes, and only possible in a closed loop.
Conventional current flows from the + terminal of the cell, around the circuit, to the − terminal.
Just as flowing water makes a water current, flowing charge makes an electric current. If charge flows through a conductor, say, a metal wire, we say there's a current in it. A torch only lights up when its switch is on, because a switch simply completes (or breaks) a conducting link between the cell and the bulb. A continuous, closed path for current is called an electric circuit; break it anywhere and the current stops.
Current is defined as the rate of flow of charge: if a net charge Q flows across a conductor's cross-section in time t, the current is I = Q/t. The SI unit of charge is the coulomb (C), and the SI unit of current is the ampere (A): one ampere means one coulomb of charge flowing per second (1 A = 1 C/1 s). Small currents are measured in milliampere (1 mA = 10⁻³ A) or microampere (1 µA = 10⁻⁶ A).
In a metallic wire, it's actually electrons that move to carry the current. But when electricity was first studied, electrons hadn't been discovered yet, so current was defined as the flow of *positive* charge. By convention, this stuck: the direction of electric current is taken as opposite to the actual direction electrons move.
An ammeter measures current in a circuit. It's always connected in series, inserted directly into the loop the current flows through, so the same current that flows through the circuit also flows through the meter.
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Electricity Class 10 | Electric current and Electric Circuit | Define the SI unit of electric current · Anjali Sharma