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The 2019 revision of the SI defined the ampere by taking the fixed numerical value of the elementary charge e to be 1.602 176 634 × 10 −19 when expressed in the unit C, which is equal to A⋅s, where the second is defined in terms of ∆ν Cs, the unperturbed ground state hyperfine transition frequency of the caesium-133 atom.
1 A Typical iPhone charger (5 W) 1.35 A Tesla coil, 0.76 meters (2 ft 6 in) high, at 200 kV and 270 kV peak [4] 2.1 A High power LED current (peak 2.7 A) [5] 5 A One typical 12 V motor vehicle headlight (typically 60 W) 9 A 230 V AC, toaster, kettle (2 kW) 10 1: 10 or 20 A 230 V AC, Europe common domestic circuit breaker rating 15 or 20 A
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m 2 ⋅s −3. [ 1 ] [ 2 ] [ 3 ] It is used to quantify the rate of energy transfer .
It has an earthing pin and two flat current-carrying pins forming an inverted V-shape (120°). The flat pins for the 10 A version measure 6.25 by 1.55 mm (0.246 by 0.061 in) and 8.0 by 1.9 mm (0.315 by 0.075 in) for the 20 A version, and are set at 30° to the vertical at a nominal pitch of 7.92 mm (0.312 in).
The ampere rapidly gained support over the ohm, as many national standards laboratories were already realizing the ampere in absolute terms using ampere balances. [16] [20] The International Electrotechnical Commission (IEC) adopted the Giorgi system with the ampere replacing the ohm in 1935, and this choice of base units is often called the ...
The coulomb was originally defined, using the latter definition of the ampere, as 1 A × 1 s. [4] The 2019 redefinition of the ampere and other SI base units fixed the numerical value of the elementary charge when expressed in coulombs and therefore fixed the value of the coulomb when expressed as a multiple of the fundamental charge.
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DC meters often measured charge in ampere hours. Since the voltage of the supply should remain substantially constant, the reading of the meter was proportional to actual energy consumed. For example, if a meter recorded that 100 ampere hours had been consumed on a 200-volt supply, then 20 kilowatt-hours of energy had been supplied. A 'Reason ...