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In electromagnetism and electronics, inductance is the property of an electrical conductor by which a change in current flowing through it induces an electromotive force in both the conductor itself〔Sears and Zemansky 1964:743〕 and in any nearby conductors by mutual inductance.〔 These effects are derived from two fundamental observations of physics: a steady current creates a steady magnetic field described by Oersted's law,〔Sears and Zemansksy 1964:671〕 and a time-varying magnetic field induces an electromotive force in nearby conductors, which is described by Faraday's law of induction.〔Sears and Zemansky 1964:671 -- "The work of Oersted thus demonstrated that magnetic effects could be produced by moving electric charges, and that of Faraday and Henry that currents could be produced by moving magnets."〕 According to Lenz's law,〔Sears and Zemansky 1964:731 -- "The direction of an induced current is such as to oppose the cause producing it".〕 a changing electric current through a circuit that contains inductance induces a proportional voltage, which opposes the change in current (self-inductance). The varying field in this circuit may also induce an e.m.f. in neighbouring circuits (mutual inductance). The term ''inductance'' was coined by Oliver Heaviside in 1886. It is customary to use the symbol ''L'' for inductance, in honour of the physicist Heinrich Lenz.〔(【引用サイトリンク】 The Physics Hypertextbook: Inductance )〕〔(【引用サイトリンク】 Molecular Expressions: Electricity and Magnetism Introduction: Inductance )〕 In the SI system, the measurement unit for inductance is the henry with the unit symbol ''H'', named in honor of Joseph Henry, who discovered inductance independently of, but not before, Faraday. ==Circuit analysis== An electronic component that is intended to add inductance to a circuit is called an inductor. Inductors are typically manufactured from coils of wire. This design delivers two desired properties, a concentration of the magnetic field into a small physical space and a linking of the magnetic field into the circuit multiple times. The relationship between the self-inductance ''L'' of an electrical circuit, the voltage ''v(t)'', and the current ''i(t)'' through the circuit is :. A voltage is induced across an inductor (back EMF), that is equal to the product of the inductor's inductance and the rate of change of current through the inductor. All circuits have, in practice, some inductance, which may have beneficial or detrimental effects. For a tuned circuit, inductance is used to provide a frequency-selective circuit. Practical inductors may be used to provide filtering, or energy storage, in a given network. The inductance per unit length of a transmission line is one of the properties that determines its characteristic impedance; balancing the inductance and capacitance of cables is important for distortion-free telegraphy and telephony. The inductance of long AC power transmission lines effects the power capacity of the line. Sensitive circuits, such as microphone and computer network cables, may utilize special cabling construction, limiting the inductive coupling between circuits. The generalization to the case of ''K'' electrical circuits with currents ''im'' and voltages ''vm'' reads : Here, inductance ''L'' is a symmetric matrix. The diagonal coefficients ''Lm,m'' are called coefficients of self-inductance, the off-diagonal elements are called coefficients of mutual inductance. The coefficients of inductance are constant, as long as no magnetizable material with nonlinear characteristics is involved. This is a direct consequence of the linearity of Maxwell's equations in the fields and the current density. The coefficients of inductance become functions of the currents in the nonlinear case. 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「inductance」の詳細全文を読む スポンサード リンク
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