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The henry (symbol H) is the unit of electrical inductance in the International System of Units. The unit is named after Joseph Henry (1797–1878), the American scientist who discovered electromagnetic induction independently of and at about the same time as Michael Faraday (1791–1867) in England.〔(【引用サイトリンク】 url = http://etcweb.princeton.edu/CampusWWW/Companion/henry_joseph.html )〕 The magnetic permeability of vacuum is 4π×10−7 H m-1 (henry per metre). The United States National Institute of Standards and Technology recommends English-speaking users of SI to write the plural as ''henries''.〔 〕 ==Definition== The inductance of an electric circuit is one henry when an electric current that is changing at one ampere per second results in an electromotive force of one volt across the inductor : :, where ''v(t)'' denotes the resulting voltage across the circuit, ''i(t)'' is the current through the circuit, and ''L'' is the inductance of the circuit. The henry is a derived unit based on four of the seven base units of the International System of Units: kilogram (kg), meter (m), second (s), and ampere (A). Expressed in combinations of SI units, the henry is:〔(【引用サイトリンク】 work = The NIST Reference on Constants, Units and Uncertainty )〕 : in which the following additional derived units occur: coulomb (C), farad (F), joule (J), weber (Wb), tesla (T), volt (V), hertz (Hz), and ohm (Ω). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Henry (unit)」の詳細全文を読む スポンサード リンク
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