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An ampere-hour or amp-hour (symbol: A⋅h or A h; often simplified as Ah) is a unit of electric charge, having dimensions of electric current multiplied by time, equal to the charge transferred by a steady current of one ampere flowing for one hour, or 3,600 coulombs. [1] [2] The commonly seen milliampere-hour (symbol: mA⋅h, mA h, often ...
The watt-second is a unit of energy, equal to the joule. One kilowatt hour is 3,600,000 watt seconds. While a watt per hour is a unit of rate of change of power with time, [iii] it is not correct to refer to a watt (or watt-hour) as a watt per hour. [36]
The dimension of power is energy divided by time. In the International System of Units (SI), the unit of power is the watt (W), which is equal to one joule per second. Other common and traditional measures are horsepower (hp), comparing to the power of a horse; one mechanical horsepower equals about 745.7 watts.
The SI derived unit of electric charge is the coulomb (C) named after French physicist Charles-Augustin de Coulomb. In electrical engineering it is also common to use the ampere-hour (A⋅h). In physics and chemistry it is common to use the elementary charge (e) as a unit.
The unit "var" is allowed by the International System of Units (SI) even though the unit var is representative of a form of power. [8] Per EU directive 80/181/EEC (the "metric directive"), the correct symbol is lower-case "var", [ 1 ] although the spellings "Var" and "VAr" are commonly seen, and "VAR" is widely used throughout the power industry.
As of the 2019 revision of the SI, the ampere is defined by fixing the elementary charge e to be exactly 1.602 176 634 × 10 −19 C, [6] [9] which means an ampere is an electric current equivalent to 10 19 elementary charges moving every 1.602 176 634 seconds or 6.241 509 074 × 10 18 elementary charges moving in a second.
The ampere is an SI base unit and electric current is a base quantity in the International System of Quantities (ISQ). [ 4 ] : 15 Electric current is also known as amperage and is measured using a device called an ammeter .
1–3 × 10 3 W tech: heat output of a domestic electric kettle: 1.1 × 10 3 W tech: power of a microwave oven: 1.366 × 10 3 W astro: power per square meter received from the Sun at the Earth's orbit: 1.5 × 10 3 W tech: legal limit of power output of an amateur radio station in the United States up to 2 × 10 3 W