Editing Caesium standard (section)

=== Electromagnetic units ===

Prior to the revision, the ampere was defined as the current needed to [[Ampère's force law|produce a force]] between 2 parallel wires 1 m apart of 0.2 [[Newton (unit)|μN]] per meter. The 2019 revision replaced this definition by giving [[elementary charge|the charge on the electron]], ''e'', the exact value {{val|1.602176634|e=-19}} coulombs. Somewhat incongruously, the coulomb is still considered a derived unit and the ampere a base unit, rather than vice versa.<ref>{{Cite web|url=https://www.bipm.org/en/history-si/ampere|title = Ampere - BIPM}}</ref> In any case, this convention entailed the following exact relationships between the SI electromagnetic units, elementary charge, and the caesium-133 hyperfine transition radiation:
* 1 [[coulomb]], C, = {{sfrac|{{val|e=19}}|{{val|1.602176634}}}} ''e''
* 1 [[ampere]], or amp, A, = 1 C/s = {{sfrac|{{val|e=9}}|{{val|1.472821982686006218}}}} ''e'' {{math|Δ''ν''<sub>Cs</sub>}}
* 1 [[volt]], V, = 1 J/C = {{sfrac|{{val|1.602176634|e=5}}|{{val|6.09110229711386655}}}} {{math|Δ''E''<sub>Cs</sub>}}/''e''
* 1 [[farad]], F, = 1 C/V = {{sfrac|{{val|6.09110229711386655|e=14}}|{{val|2.566969966535569956}}}} ''e''<sup>2</sup>/{{math|Δ''E''<sub>Cs</sub>}}
* 1 [[Ohm (unit)|ohm]], Ω, = 1 V/A = {{sfrac|{{val|2.359720966701071721258310212|e=-4}}|{{val|6.09110229711386655}}}} {{math|Δ''E''<sub>Cs</sub>}}/{{math|Δ''ν''<sub>Cs</sub>}} ''e''<sup>2</sup> = {{sfrac|{{val|2.359720966701071721258310212|e=-4}}|{{val|6.09110229711386655}}}} ''h''/''e''<sup>2</sup>
* 1 [[Siemens (unit)|siemens]], S, = 1/Ω = {{sfrac|{{val|6.09110229711386655|e=4}}|{{val|2.359720966701071721258310212}}}} ''e''<sup>2</sup>/''h''
* 1 [[Weber (unit)|weber]], Wb, = 1 V s = {{sfrac|{{val|1.602176634|e=15}}|{{val|6.62607015}}}} {{math|Δ''E''<sub>Cs</sub>}} {{math|Δ''t''<sub>Cs</sub>}}/''e'' = {{sfrac|{{val|1.602176634|e=15}}|{{val|6.62607015}}}} ''h''/''e''
* 1 [[Tesla (unit)|tesla]], T, = 1 Wb/m<sup>2</sup> = {{sfrac|{{val|1.43996454705862285832702376|e=12}}|{{val|5.59932604907689089550702935}}}} {{math|Δ''E''<sub>Cs</sub>}} {{math|Δ''t''<sub>Cs</sub>}}/''e'' {{math|Δ''λ''<sub>Cs</sub>}}<sup>2</sup> = {{sfrac|{{val|1.43996454705862285832702376|e=12}}|{{val|5.59932604907689089550702935}}}} ''E''/''e c'' {{math|Δ''λ''<sub>Cs</sub>}}
* 1 [[Henry (unit)|henry]], H, = Ω s = {{sfrac|{{val|2.359720966701071721258310212|e=6}}|{{val|6.62607015}}}} ''h'' {{math|Δ''t''<sub>Cs</sub>}}/''e''<sup>2</sup>