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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.
In the International System of Units (SI), electric current is expressed in units of ampere (sometimes called an "amp", symbol A), which is equivalent to one coulomb per second. The ampere is an SI base unit and electric current is a base quantity in the International System of Quantities (ISQ).
Symbol [1] Name of quantity Unit name Symbol Base units E energy: joule: J = C⋅V = W⋅s kg⋅m 2 ⋅s −2: Q electric charge: coulomb: C A⋅s I electric current: ampere
The ampere may be expressed directly in terms of the defining constants as: 1 A = e Δν Cs / (1.602 176 634 × 10 −19)(9 192 631 770) For illustration, this is equivalent to defining one coulomb to be an exact specified multiple of the elementary charge. 1 C = e / 1.602 176 634 × 10 −19
One faraday equals 9.648 533 212... × 10 4 coulombs. [5] In terms of the Avogadro constant (N A), one coulomb is equal to approximately 1.036 × 10 −5 mol × N A elementary charges. Every farad of capacitance can hold one coulomb per volt across the capacitor. One ampere hour equals 3600 C, hence 1 mA⋅h = 3.6 C.
The henry (symbol: H) is the unit of electrical inductance in the International System of Units (SI). [1] If a current of 1 ampere flowing through a coil produces flux linkage of 1 weber turn, that coil has a self-inductance of 1 henry. The unit is named after Joseph Henry (1797–1878), the American scientist who discovered electromagnetic induction independently of and at about the same ...
The ohm (Ω) is equal to one volt per ampere (1 V⋅A −1). The siemens (S) is equal to one ampere per volt (1 A⋅V −1). The henry (H) is equal to one weber per ampere (1 Wb⋅A −1). The degree Celsius (°C) is equal to one kelvin (1 K). The lumen (lm) is equal to one candela-steradian (1 cd⋅sr).
For a device with a conductance of one siemens, the electric current through the device will increase by one ampere for every increase of one volt of electric potential difference across the device. The conductance of a resistor with a resistance of five ohms, for example, is (5 Ω) −1, which is equal to a conductance of 200 mS.