Ohm (unit)

Ohm
A laboratory one-Ohm standard resistor.
Unit system	SI derived unit
Unit of	Electrical resistance
Symbol	Ω
Named after	Georg Ohm
In SI base units:	kg⋅m2⋅s−3⋅A−2

The ohm (symbol: Ω) is the SI derived unit of electrical resistance, named after German physicist Georg Simon Ohm. Although several empirically derived standard units for expressing electrical resistance were developed in connection with early telegraphy practice, the British Association for the Advancement of Science proposed a unit derived from existing units of mass, length and time and of a convenient size for practical work as early as 1861. The definition of the ohm was revised several times. Today the definition of the ohm is expressed from the quantum Hall effect.

The ohm is defined as an electrical 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.

${\displaystyle \Omega ={\dfrac {\mbox{V}}{\mbox{A}}}={\dfrac {\mbox{1}}{\mbox{S}}}={\dfrac {\mbox{W}}{{\mbox{A}}^{2}}}={\dfrac {{\mbox{V}}^{2}}{\mbox{W}}}={\dfrac {\mbox{s}}{\mbox{F}}}={\dfrac {{\mbox{J}}\cdot {\mbox{s}}}{{\mbox{C}}^{2}}}={\dfrac {{\mbox{kg}}\cdot {\mbox{m}}^{2}}{{\mbox{s}}\cdot {\mbox{C}}^{2}}}={\dfrac {\mbox{J}}{{\mbox{s}}\cdot {\mbox{A}}^{2}}}={\dfrac {{\mbox{kg}}\cdot {\mbox{m}}^{2}}{{\mbox{s}}^{3}\cdot {\mbox{A}}^{2}}}}$