ampère

The ampere, abbreviated as amp or symbol A, is the SI base unit of electric current. It measures the rate at which electric charge flows. The term is named after André-Marie Ampère, a French physicist who helped develop the science of electromagnetism.

Historically, the ampere was defined in terms of the mechanical force between two long, parallel conductors. Today, the definition was revised in 2019 to anchor the unit to a fundamental constant: the elementary charge. Specifically, the ampere is defined by fixing the elementary charge e to exactly 1.602176634×10^-19 coulombs. Under this definition, one ampere is the current corresponding to a flow of one coulomb of charge per second. This change links the ampere to the second and to fundamental constants, providing greater stability for precise measurements and standards worldwide.

In practical use, currents are measured in amperes and smaller or larger multiples such as milliamperes (mA), microamperes (µA), nanoamperes (nA), or kilamperes (kA). The ampere is essential in describing electrical circuits, power systems, and electronic devices. Electric current is also the source of magnetic effects described by electromagnetism; the strength of magnetic fields around conductors is proportional to the current in amperes.

In summary, the ampere is the modern SI unit for electric current, defined by a fixed value of elementary charge and serving as a fundamental parameter in science and engineering.