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An inductor is usually constructed as a coil of conducting material, typically copper wire. A core of ferrous material is sometimes used, which increases the inductance. Inductors can also be built on integrated circuits using the same processes that are used to make computer chips. In these cases, aluminum is typically used as the conducting material. However, it is rare that actual inductors are built on ICs; practical constraints make it far more common to use a circuit called a " gyrator" which uses a capacitor to behave as if it were an inductor.
Smaller inductors used for very high frequencies are sometimes made with a wire passing through a ferrite cylinder or bead.
Inductance is a physical characteristic of an inductor. See inductance.
The energy (measured in joules, in SI) stored in an inductor is equal to the amount of work required to establish the current flowing through the inductor, and therefore the magnetic field. This is given by:
where I is the current flowing through the inductor.
An inductor only resists changes in current. An ideal inductor does not offer any resistance to direct current, except when the current is switched on and off, in which case it makes the change more gradual. However, all real-world inductors are constructed from material with finite electrical resistance, which opposes even direct current.
In general, the relationship between the time-varying voltage v(t) across an inductor with inductance L and the time-varying current i(t) passing through it is described by the differential equation
When a sinusoidal alternating current (AC) flows through an inductor, a sinusoidal alternating voltage (or electromotive forceAn electromotive force ( emf is the "force", measured in volts, that is produced by interaction between a current and a magnetic field, at least one of which is changing. Since the word " force" now has a very specific meaning in physics, and an emf is no, abbr. emf) is induced. The amplitude of the emf is related to the amplitude of the current and to the frequency of the sinusoid by the following equation.
where ω is the angular frequencyIn physics (specifically mechanics and electrical engineering), angular frequency ω (also called angular speed is a scalar measure of rotation rate. Angular frequency is the magnitude of the vector quantity angular velocity . The term angular freque of the sinusoid defined in terms of the frequency f as
Inductive reactance is defined as:
where XL is the inductive reactance, ω is the angular frequencyIn physics (specifically mechanics and electrical engineering), angular frequency ω (also called angular speed is a scalar measure of rotation rate. Angular frequency is the magnitude of the vector quantity angular velocity . The term angular freque, f is the frequency in HertzHertz is also the name of a car rental company. See The Hertz Corporation''. The hertz (symbol Hz is the SI unit of frequency. It is named in honour of the German physicist Heinrich Rudolf Hertz who made some important contributions to science in the fiel, and L is the inductance.
Inductive reactance is the positive imaginary component of impedanceIn electrical engineering, impedance is a measure for the manner and degree a component resists the flow of electrical current if a given voltage is applied. It is denoted by the symbol Z and is measured in ohms. Impedance differs from simple resistance i.
The complex impedance of an inductor is then given by:
where j is the imaginary unitIn mathematics, the imaginary unit i allows the real number system R to be extended to the complex number system C . Its precise definition is dependent upon the particular method of extension. The primary motivation for this extension is the fact that no.