Ampères

The ampere, abbreviated A, is the SI base unit of electric current. It is defined by fixing the elementary charge e to exactly 1.602176634×10−19 coulombs, such that one ampere is the current that transports one coulomb of charge per second. The unit is named after André-Marie Ampère, a French physicist and one of the founders of electromagnetism.

Historically, the ampere was defined in terms of the force between two infinitely long, parallel conductors separated by one meter in vacuum, with a current that would produce a specified force per unit length. In 2019 the definition was revised to rely on fundamental constants rather than a mechanical standard. In practice, national metrology institutes realize the ampere through quantum electrical standards that relate charge transfer to time, enabling direct traceability to the elementary charge.

Submultiples and multiples exist, including milliampere (mA), microampere (µA), nanoampere (nA), and kiloampere (kA). The ampere is widely used to specify currents in electrical circuits, power devices, and electronic equipment. Large currents are common in power distribution and industrial contexts, while small currents appear in electronics and sensors. The measurement of current emphasizes the rate of charge flow, independent of the energy carried by individual charges.

The ampere is closely linked to the broader study of electromagnetism. Ampère’s circuital law describes how electric currents generate magnetic fields and underpins many practical devices, from transformers to motors. The unit remains a fundamental parameter in designing and analyzing electrical systems across science and engineering.