1.2 A") and the charge accumulated (or passed through a circuit) over a period of time is expressed in coulombs (as in "the battery charge is "). The relation of the ampere (C/s) to the coulomb is the same as that of the watt (J/s) to the joule. Units derived from the ampere The international system of units (SI) is based on 7 SI base units the second, metre, kilogram, kelvin, ampere, mole, and candela representing 7 fundamental types of physical quantity, or "dimensions", (time, length, mass, temperature, electrical current, amount of substance, and luminous intensity respectively) with all other SI units being defined using these. These SI derived units can either be given special names e.g. watt, volt, lux, etc. or defined in terms of others, e.g. metre per second. The units with special names derived from the ampere are: There are also some SI units that are frequently used in the context of electrical engineering and electrical appliances, but can be defined independently of the ampere, notably the hertz, joule, watt, candela, lumen, and lux. SI prefixes Like other SI units, the ampere can be modified by adding a prefix that multiplies it by a power of 10. See also Ammeter Ampacity (current-carrying capacity) Electric current Electric shock Hydraulic analogy Magnetic constant Orders of magnitude (current) References External links The NIST Reference on Constants, Units, and Uncertainty NIST Definition of ampere and μ0 SI base units Units of electric current