{"url":"https:\/\/siunits.stuchalk.domains.unf.edu\/api\/baseunit\/ampere","pid":"si:unit:ampere:2019","name":"ampere","urlname":"ampere","definition":"The ampere, symbol *A<\/em>, is the SI unit of electric current. It is defined by taking the fixed numerical value of the elementary charge **e<\/em> to be 1.602 176 634 x 10*^{-19<\/sup> when expressed in the unit C<\/em>, which is equal to A s<\/em>, where the second is defined in terms of Δν<\/em>Cs<\/sub>.","source":"SI Brochure 9th Ed. 2019, p 132","source_url":null,"siunit":null,"startdate":"2019-05-20","enddate":null,"status":"Valid","reference":"CGPM Resolution 1 of the 26th CGPM (2018) \"On the revision of the International System of Units (SI)<\/a>\"","reference_url":null,"year":2019,"names":"ampere:ampere","pinfo":null,"notes":{"1":"This definition implies the exact relation \\(e = 1.602\\:176\\:634\\:10^{-19} {A\\:s}\\). Inverting this relation gives an exact expression for the unit ampere in terms of the defining constants \\(e\\) and \\(\\Delta\\nu_{\\rm{Cs}}\\):\r\n$$1\\ {\\rm{A}} = (\\frac{e}{1.602\\:176\\:634 \\times 10^{-19}}) {\\rm{s}}^{-1}$$\r\nwhich is equal to\r\n$$1\\ {\\rm{A}} = \\frac{1}{(9\\:192\\:631\\:770)(1.602\\:176\\:634 \\times 10^{-19})}\\Delta\\nu_{\\rm{Cs}}e \\approx 6.789\\:687 \\times 10^{8}\\Delta\\nu_{\\rm{Cs}}e.$$","2":"The effect of this definition is that one ampere is the electric current corresponding to the flow of \\(1\/(1.602\\:176\\:634 \\times 10^{-19})\\) elementary charges per second.","3":"The previous definition of the ampere was based on the force between two current carrying conductors and had the effect of fixing the value of the vacuum magnetic permeability \\(\\mu_{0}\\) (also known as the magnetic constant) to be exactly \\(4\\pi \\times 10^{-7}\\ {H\\ m}^{-1} = 4\\pi \\times 10^{-7}\\ {N\\ A}^{-2}\\), where \\(H\\) and \\(N\\) denote the coherent derived units henry and newton, respectively. The new definition of the ampere fixes the value of \\(e\\) instead of \\(\\mu_{0}\\). As a result, \\(\\mu_{0}\\) must be determined experimentally.","4":"It also follows that since the vacuum electric permittivity \\(\\varepsilon_{0}\\) (also known as the electric constant), the characteristic impedance of vacuum \\(Z_{0}\\), and the admittance of vacuum \\(Y_{0}\\) are equal to \\(1\/\\mu_{0}c^{2}\\), \\(\\mu_{0}c\\), and \\(1\/\\mu_{0}c\\), the values of \\(\\epsilon_{0}\\), \\(Z_{0}\\) and \\(Y_{0}\\) must now also be determined experimentally, and are affected by the same relative standard uncertainty as \\(\\mu_{0}\\) since \\(c\\) is exactly known. The product \\(\\varepsilon_{0}\\mu_{0} = 1\/c^{2}\\) and quotient \\(Z_{0}\/\\mu_{0} = c\\) remain exact. At the time of adopting the present definition of the ampere, \\(\\mu_{0}\\) was equal to \\(4\\pi \\times 10^{-7}\\ {\\rm{H\\ m^{-1}}}\\) with a relative uncertainty of \\(2.3 \\times 10^{-10}\\)."},"related":[{"relationship":"hasUnitSymbol","weburl":"https:\/\/siunits.stuchalk.domains.unf.edu\/si\/definition\/unitsymbol\/A","apurl":"https:\/\/siunits.stuchalk.domains.unf.edu\/api\/unitsymbol\/A"},{"relationship":"hasDefiningEquation","weburl":"https:\/\/siunits.stuchalk.domains.unf.edu\/si\/definition\/definingequation\/ampere_equation","apurl":"https:\/\/siunits.stuchalk.domains.unf.edu\/api\/definingequation\/ampere_equation"}],"date":"2024-06-18T14:35:10+00:00"}}