ampere

Ampere refers to both the French physicist André-Marie Ampère and the SI unit of electric current named in his honor. The term is widely used in physics and engineering to describe current and magnetic phenomena, and the unit is one of the base units of the International System of Units (SI).

André-Marie Ampère (1775–1836) was a French mathematician and physicist who helped develop the science of electromagnetism. He conducted experiments and formulated theories about the relationship between electricity and magnetism, proposing that electric currents produce magnetic effects. His ideas laid important groundwork for later advances by Oersted, Faraday, and Maxwell and helped establish a mathematical framework for describing magnetic forces generated by currents.

The ampere (symbol A) is the SI base unit of electric current. It is traditionally defined as the flow of one coulomb of charge per second. In 2019, the definition was redefined by fixing the elementary charge e to exactly 1.602176634×10−19 coulombs, making the ampere a derived unit based on fundamental constants. Practical realization relies on quantum electrical standards, such as the Josephson effect for voltage and the quantum Hall effect for resistance, allowing precise realization of current through well-defined voltage and resistance standards.

Ampere’s law is a key principle in magnetism stating that the line integral of the magnetic field around a closed loop is proportional to the current passing through the loop. In Maxwell’s equations, Ampere’s law is extended by the displacement current term, linking changing electric fields to magnetic effects and forming the foundation of modern electrodynamics.