This page documents an OPTIMADE Unit Definition. See https://schemas.optimade.org/ for more information.

**ID: https://schemas.optimade.org/defs/v1.2/units/si/general/ohm**

`ohm`

**Unit name:** ohm

**Latin symbol:** ohm

**Display symbol:** Ω

**Description:** A unit for electrical resistance equal to kg·m²·s⁻³·A⁻² using the current, or one of the historical, definitions of the SI units.

"The ohm is the electrical resistance that exists between two points of a conductor when a constant potential difference of one volt, applied between these two points, produces a current of one ampere in the conductor, provided that the conductor is not the seat of any electromotive force." [9th CGPM meeting in 1946]

The ohm was defined at the 9th CGPM Meeting in 1946, included in SI at the 11th CGPM meeting in 1960, resolution 12, implicitly redefined via the redefinitions of the second at the 13th CGPM Meeting in 1967, resolution 1, the metre at the 17th CGPM meeting (1983), resolution 1, and the kilogram and ampere at the 26th CGPM Meeting (2018), resolution 1.

This is a generalized definition taken to reference the current, or one of the historical, SI unit definitions. This definition is intended for situations when it is not possible to be more precise, e.g., in contexts where data have been collected that uses different historical SI definitions.

**Resources:**

- Definition at the 9th CGPM meeting (1948)
- Definition and establishment of the SI unit system at the 11th CGPM meeting (1960), resolution 12.
- Redefinition of the metre at the 17th CGPM meeting (1983), resolution 1
- Redefinition of the second in the 13th CGPM Meeting (1967), resolution 1
- Redefinition of the kilogram and the ampere at the 26th CGPM Meeting (2018), resolution 1
- Wikipedia article describing the unit

**Compatibility:** (other definitions that are covered by the above definition)

`https://schemas.optimade.org/defs/v1.2/units/si/1960/named/ohm`

`https://schemas.optimade.org/defs/v1.2/units/si/1967/named/ohm`

`https://schemas.optimade.org/defs/v1.2/units/si/1983/named/ohm`

`https://schemas.optimade.org/defs/v1.2/units/si/2019/named/ohm`

**JSON definition:**

```
{
"$id": "https://schemas.optimade.org/defs/v1.2/units/si/general/ohm",
"$schema": "https://schemas.optimade.org/meta/v1.2/optimade/physical_unit_definition.json",
"title": "ohm",
"symbol": "ohm",
"display-symbol": "\u03a9",
"description": "A unit for electrical resistance equal to kg\u00b7m\u00b2\u00b7s\u207b\u00b3\u00b7A\u207b\u00b2 using the current, or one of the historical, definitions of the SI units.\n\n\"The ohm is the electrical resistance that exists between two points of a conductor when a constant potential difference of one volt, applied between these two points, produces a current of one ampere in the conductor, provided that the conductor is not the seat of any electromotive force.\" [9th CGPM meeting in 1946]\n\nThe ohm was defined at the 9th CGPM Meeting in 1946, included in SI at the 11th CGPM meeting in 1960, resolution 12, implicitly redefined via the redefinitions of the second at the 13th CGPM Meeting in 1967, resolution 1, the metre at the 17th CGPM meeting (1983), resolution 1, and the kilogram and ampere at the 26th CGPM Meeting (2018), resolution 1.\n\nThis is a generalized definition taken to reference the current, or one of the historical, SI unit definitions.\nThis definition is intended for situations when it is not possible to be more precise, e.g., in contexts where data have been collected that uses different historical SI definitions.",
"compatibility": [
"https://schemas.optimade.org/defs/v1.2/units/si/1960/named/ohm",
"https://schemas.optimade.org/defs/v1.2/units/si/1967/named/ohm",
"https://schemas.optimade.org/defs/v1.2/units/si/1983/named/ohm",
"https://schemas.optimade.org/defs/v1.2/units/si/2019/named/ohm"
],
"resources": [
{
"relation": "Definition at the 9th CGPM meeting (1948)",
"resource-id": "https://www.bipm.org/en/committees/cg/cgpm/9-1948"
},
{
"relation": "Definition and establishment of the SI unit system at the 11th CGPM meeting (1960), resolution 12.",
"resource-id": "https://www.bipm.org/en/committees/cg/cgpm/11-1960/resolution-12"
},
{
"relation": "Redefinition of the metre at the 17th CGPM meeting (1983), resolution 1",
"resource-id": "https://www.bipm.org/en/committees/cg/cgpm/17-1983/resolution-1"
},
{
"relation": "Redefinition of the second in the 13th CGPM Meeting (1967), resolution 1",
"resource-id": "https://www.bipm.org/en/committees/cg/cgpm/13-1967/resolution-1"
},
{
"relation": "Redefinition of the kilogram and the ampere at the 26th CGPM Meeting (2018), resolution 1",
"resource-id": "https://www.bipm.org/en/committees/cg/cgpm/26-2018/resolution-1"
},
{
"relation": "Wikipedia article describing the unit",
"resource-id": "https://en.wikipedia.org/wiki/Ohm"
}
],
"defining-relation": {
"base-units": [
{
"symbol": "A",
"id": "https://schemas.optimade.org/defs/v1.2/units/si/general/ampere"
},
{
"symbol": "kg",
"id": "https://schemas.optimade.org/defs/v1.2/units/si/general/kilogram"
},
{
"symbol": "m",
"id": "https://schemas.optimade.org/defs/v1.2/units/si/general/metre"
},
{
"symbol": "s",
"id": "https://schemas.optimade.org/defs/v1.2/units/si/general/second"
}
],
"base-units-expression": "A^-2*kg*m^2*s^-3"
},
"x-optimade-definition": {
"label": "ohm_si_general",
"kind": "unit",
"format": "1.2",
"version": "1.2.0",
"name": "ohm"
}
}
```