Resolution 2 of the 41st CIPM (1946)

Definitions of electric units


  1. A) Definitions of the mechanical units which enter the definitions of electric units:

    Unit of force - The unit of force [in the MKS (metre, kilogram, second) system] is the force which gives to a mass of 1 kilogram an acceleration of 1 metre per second, per second.

    Joule (unit of energy or work) - The joule is the work done when the point of application of 1 MKS unit of force [newton] moves a distance of 1 metre in the direction of the force.

    Watt (unit of power) - The watt is the power which in one second gives rise to energy of 1 joule.

    B) Definitions of electric units:

    The Comité International des Poids et Mesures (CIPM) accepts the following propositions which define the theoretical value of the electric units:

    Ampere (unit of electric current) - The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2 ´ 10-7 MKS unit of force [newton] per metre of length.

    Volt (unit of potential difference and of electromotive force) - The volt is the potential difference between two points of a conducting wire carrying a constant current of 1 ampere, when the power dissipated between these points is equal to 1 watt.

    Ohm (unit of electric resistance) - The ohm is the electric resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere, the conductor not being the seat of any electromotive force.

    Coulomb (unit of quantity of electricity) - The coulomb is the quantity of electricity carried in 1 second by a current of 1 ampere.

    Farad (unit of capacitance) - The farad is the capacitance of a capacitor between the plates of which there appears a potential difference of 1 volt when it is charged by a quantity of electricity of 1 coulomb.

    Henry (unit of electric inductance) - The henry is the inductance of a closed circuit in which an electromotive force of 1 volt is produced when the electric current in the circuit varies uniformly at the rate of 1 ampere per second.

    Weber (unit of magnetic flux) - The weber is the magnetic flux which, linking a circuit of one turn, would produce in it an electromotive force of 1 volt if it were reduced to zero at a uniform rate in 1 second.

reference The reader should note that the official version of this Resolution is the French text

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