Symbol A. The SI unit of electric current. The constant current that, maintained in two straight parallel infinite conductors of negligible cross section placed one metre apart in a vacuum, would produce a force between the conductors of 2 × 10⁻⁷ N m⁻¹. This definition replaced the earlier international ampere, defined as the current required to deposit 0.001 118 00 gram of silver from a solution of silver nitrate in one second. The unit is named after A. M. Ampère. Because very small electrical circuits can manipulate individual electrons, it has been suggested that future definitions of the ampere will be in terms of quantities associated with such circuits.