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IEVref: | 112-02-07 | ID: | |

Language: | en | Status: Standard | |

Term: | ampere | ||

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Symbol: | A | ||

Definition: | SI unit of electric current, equal to the electric current corresponding to the flow of (1/1,602 176 634) × 10^{19} elementary electric charges per second
Note 1 to entry: The definition in the SI Brochure is: "The ampere, symbol A, is the SI unit of electric current. It is defined by taking the fixed numerical value of the elementary charge Note 2 to entry: The definition of the ampere in IEV 112-02-07:2010-01 was: "SI unit of electric current, equal to the direct current which, if maintained constant in two straight parallel conductors of infinite length, of circular cross-section with negligible area, and placed 1 metre apart in vacuum, would produce between these conductors a force per length equal to 2 × 10 Note 3 to entry: The new definition of the ampere fixes the value of the elementary charge Note 4 to entry: The ampere is one of the seven SI base units: second (s), metre (m), kilogram (kg), ampere (A), kelvin (K), mole (mol) and candela (cd). | ||

Publication date: | 2020-12 | ||

Source: | SI Brochure, 9th edition, 2019, 2.3.1, modified – The definition in the SI Brochure has been revised to comply with the IEV rules. Notes 1 to 4 to entry have been added. | ||

Replaces: | 112-02-07:2010-01 | ||

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Note 1 to entry: The definition in the SI Brochure is: "The ampere, symbol A, is the SI unit of electric current. It is defined by taking the fixed numerical value of the elementary charge *e* to be 1,602 176 634 × 10^{−19} when expressed in the unit C, which is equal to A s, where the second is defined in terms of Δ*ν*_{Cs}."

Note 2 to entry: The definition of the ampere in IEV 112-02-07:2010-01 was: "SI unit of electric current, equal to the direct current which, if maintained constant in two straight parallel conductors of infinite length, of circular cross-section with negligible area, and placed 1 metre apart in vacuum, would produce between these conductors a force per length equal to 2 × 10^{−7} N/m".

Note 3 to entry: The new definition of the ampere fixes the value of the elementary charge *e* instead of that of the magnetic constant, *μ*_{0}. As a consequence, the value of *μ*_{0} has to be determined experimentally.

Note 4 to entry: The ampere is one of the seven SI base units: second (s), metre (m), kilogram (kg), ampere (A), kelvin (K), mole (mol) and candela (cd).