My Cart # Finding A Current Current is the rate at which electrons flow past a point in a complete electrical circuit. At its most basic, current = flow.

An ampere (AM-pir), or amp, is the international unit used for measuring current. It expresses the quantity of electrons (sometimes called "electrical charge") flowing past a point in a circuit over a given time.

A current of 1 ampere means that 1 coulomb of electrons—that's 6.24 billion billion (6.24 x 1018) electrons—is moving past a single point in a circuit in 1 second. The calculation is similar to measuring water flow: how many gallons pass a single point in a pipe in 1 minute (gallons per minute, or GPM).

Symbols used for amps:

A = amperes, for a large amount of current (1.000).
mA = milliamperes, a thousandth of an amp (0.001).
µA = microamperes, a millionth of an amp (0.000001).

In formulas such as Ohm's Law, current is also represented by I (for intensity).

Amps are named for French mathematician/physicist Andrè-Marie Ampére (1775-1836), credited for proving:

• A magnetic field is generated around a conductor as current passes through it.
• The strength of that field is directly proportional to the amount of current flowing.

Electrons flow through a conductor (typically a metal wire, usually copper) when two prerequisites of an electric circuit are met:

1. The circuit includes an energy source (a battery, for instance) that produces voltage. Without voltage, electrons move randomly and fairly evenly within a wire, and current cannot flow. Voltage creates pressure that drives electrons in a single direction.
2. The circuit forms a closed, conducting loop through which electrons can flow, providing energy to any device (a load) connected to the circuit. A circuit is closed (complete) when a switch is turned to the ON, or closed, position (see diagram at the top of this page).

Current, like voltage, can be direct or alternating.

Direct current (dc):

• Represented by the symbols or on a digital multimeter.
• Flows only in one direction.
• Common source: batteries or dc generator.

Alternating current (ac):

• Represented by the symbols or on a digital multimeter.
• Flows in a sine wave pattern (shown below); reverses direction at regular intervals.