Ampèren

Ampèren is the SI base unit of electric current. Its symbol is A. The unit is named after the French physicist André-Marie Ampère, who made foundational contributions to the study of electromagnetism. In everyday use, the ampere quantifies the rate at which electric charge flows through a conductor.

Historically, the ampere was defined as the constant current that would produce a specific force between two infinitely long, parallel conductors separated by one meter in vacuum. Since 2019, the SI definition has been fixed by fixing the elementary charge e to exactly 1.602176634×10−19 coulombs. Under this definition, one ampere corresponds to a flow of one coulomb of charge per second, i.e., 1 A = 1 C/s. This redefinition ties the ampere to fundamental physical constants rather than a mechanical setup.

Realization and measurement of the ampere rely on precision electrical standards and quantum effects. Modern practice uses highly accurate charge-transfer measurements and quantum electrical standards to realize and realize traceable currents. In practice, current values in circuits are observed and controlled using calibrated instruments, and in many contexts the current is expressed in submultiples such as milliampere (mA) or microampere (µA), as well as in larger units like kiloampere (kA) for high-power applications.

The ampere is essential in electrical engineering and physics, underpinning formulas such as Ohm’s law and various electromagnetic laws. It serves as the reference scale for current measurements in laboratories and industry, linking observable phenomena to precise, universally defined quantities.