Ampère

Ampère is a unit of electric current, named after the French physicist André-Marie Ampère. It is one of the seven base units in the International System of Units (SI). The symbol for the ampere is "A".

Definition

The ampere is defined by taking the fixed numerical value of the elementary charge e to be 1.602176634 × 10⁻¹⁹ when expressed in the unit C, which is equal to A.s, where the second is defined in terms of Δν_Cs.

History

The ampere was originally defined as one tenth of the unit of electric current in the centimetre–gram–second system of units. That unit, now known as the abampere, was defined as the amount of current that generates a force of two dynes per centimetre of length between two wires one centimetre apart. The size of the unit was chosen so that the units derived from it in the MKS system of units would be conveniently sized.

Realization

The standard ampere is most accurately realized using a Watt balance, but is in practice maintained via Ohm's law from the units of electromotive force and resistance, the volt and the ohm, since the latter two can be tied to physical phenomena that can be independently reproduced.

See also

• Coulomb
• Electric current
• Ohm's law
• SI derived unit
• Volt