Q: Was an ampere then defined as one coulomb of charge per second? ¶
Q: Is an ampere approximately equivalent to 6.2415093×1018 elementary charges moving past a boundary in one second? ¶
Q: Is an ampere that constant current which? ¶
A: Yes, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in vacuum, would produce between these conductors a force equal to 2×10−7 newtons per metre of length.
Q: Was an ampere originally defined as one tenth of the unit of electric current in the centimetre–gram–second system of units? ¶
Q: Is an ampere most accurately realized using a watt balance? ¶
A: Yes, 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 are relatively easy to reproduce, the Josephson junction and the quantum Hall effect, respectively.