Electric current: a flow of charges

A closed circuit for it to work

For an electric current to flow, a closed circuit is required: a power source (battery, cell, etc.) connected to one or more loads (lamp, motor, etc.) via conductive wires, with no breaks. As soon as the circuit is open (switch open, wire cut), no current flows.

What does the current carry?

In a metal wire, electric current corresponds to the orderly movement of electric charges (electrons) along the circuit. The more electrons that pass through a point in the circuit in one second, the greater the current.

Current: a measurable quantity

Electric current, denoted by I, measures this flow of charges. It is expressed in amperes, symbol A, in honour of the physicist André-Marie Ampère. Submultiples are also used:

Unit	Symbol	Equivalence
ampere	A	base unit
milliampere	mA	1 A = 1000 mA
microampere	microA	1 mA = 1000 microA

A useful analogy

Electric current can be compared to water flowing through a pipe: the current is similar to the water flow rate (the volume passing through every second). A high flow rate corresponds to a high current, whilst a trickle of water corresponds to a low current.

A pitfall to avoid

Do not confuse current (I, in amperes) with voltage (U, in volts): these are two different quantities. Current describes the flow of charge, whilst voltage describes the difference in electric potential between two points in the circuit.