Resolution 2 of the 41st CIPM (1946)
Definitions of electric units
- 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 kilograman acceleration of 1 metreper second, per second.
Joule (unit of energy or work) - The joule is the work done when the point of application of
1 MKSunit of force [newton] moves a distance of 1 metrein the direction of the force.
Watt (unit of power) - The watt is the power which in one second gives rise to energy of
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 metreapart in vacuum, would produce between these conductors a force equal to 2 ´ 10-7MKS 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 secondby 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 voltwhen 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 voltis produced when the electric current in the circuit varies uniformly at the rate of 1 ampereper 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 voltif it were reduced to zero at a uniform rate in 1 second.