An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when an electric current flows through it. An inductor typically consists of an insulated wire wound into a coil. When the current flowing through the coil changes, the time-varying magnetic field induces an electromotive force (emf), or voltage, in the conductor, described by Faraday's law of induction. According to Lenz's law, the induced voltage has a polarity (direction) which opposes the change in current that created it. As a result, inductors oppose any changes in current through them. An inductor is characterized by its inductance, which is the ratio of the voltage to the rate of change of current. In the International System of Units (SI), the unit of inductance is the henry (H) named for 19th century American scientist Joseph Henry. In the measurement of magnetic circuits, it is equivalent to weber/ampere. Inductors have values that typically range from 1 μH (10−6 H) to 20 H. Many inductors have a magnetic core made of iron or ferrite inside the coil, which serves to increase the magnetic field and thus the inductance. Along with capacitors and resistors, inductors are one of the three passive linear circuit elements that make up electronic circuits. Inductors are widely used in alternating current (AC) electronic equipment, particularly in radio equipment. They are used to block AC while allowing DC to pass; inductors designed for this purpose are called chokes. They are also used in electronic filters to separate signals of different frequencies, and in combination with capacitors to make tuned circuits, used to tune radio and TV receivers. The term inductor seems to come from Heinrich Daniel Ruhmkorff, who called the induction coil he invented in 1851 an inductorium.
Description
An electric current flowing through a conductor generates a magnetic field surrounding it. The magnetic flux linkage Φ B {\displaystyle \Phi _{\mathbf {B} }} generated by a given current I {\displaystyle I} depends on the geometric shape of the circuit. Their ratio defines the inductance L {\displaystyle L} . Thus
L := Φ B I {\displaystyle L:={\frac {\Phi _{\mathbf {B} }}{I}}} . The inductance of a circuit depends on the geometry of the current path as well as the magnetic permeability of nearby materials. An inductor is a component consisting of a wire or other conductor shaped to increase the magnetic flux through the circuit, usually in the shape of a coil or helix, with two terminals. Winding the wire into a coil increases the number of times the magnetic flux lines link the circuit, increasing the field and thus the inductance. The more turns, the higher the inductance. The inductance also depends on the shape of the coil, separation of the turns, and many other factors. By adding a "magnetic core" made of a ferromagnetic material like iron inside the coil, the magnetizing field from the coil will induce magnetization in the material, increasing the magnetic flux. The high permeability of a ferromagnetic core can increase the inductance of a coil by a factor of several thousand over what it would be without it.
Constitutive equation Any change in the current through an inductor creates a changing flux, inducing a voltage across the inductor. By Faraday's law of induction, the voltage E {\displaystyle {\mathcal {E}}} induced by any change in magnetic flux through the circuit is given by
E = − d Φ B d t {\displaystyle {\mathcal {E}}=-{\frac {d\Phi _{\mathbf {B} }}{dt}}} . Reformulating the definition of L above, we obtain
Φ B = L I {\displaystyle \Phi _{\mathbf {B} }=LI} . It follows that
E = − d Φ B d t = − d d t ( L I ) {\displaystyle {\mathcal {E}}=-{\frac {d\Phi _{\mathbf {B} }}{dt}}=-{\frac {d}{dt}}(LI)}
if L is independent of time, current and magnetic flux linkage. Thus, inductance is also a measure of the amount of electromotive force (voltage) generated for a given rate of change of current. This is usually taken to be the constitutive relation (defining equation) of the inductor.
Because the induced voltage is positive at the current's entrance terminal, the inductor's current–voltage relationship is often expressed without a negative sign by using the current's exit terminal as the reference point for the voltage V ( t ) {\displaystyle V(t)} at the current's entrance terminal (as labeled in the schematic). The current–voltage relationship is then:
which can be rewritten as:As with any antiderivative, a constant of integration is added to represent the initial current I(t0). The dual of the inductor is the capacitor, which stores energy in an electric field rather than a magnetic field. Its current–voltage relation replaces L with the capacitance C and has current and voltage swapped from these equations.
Lenz's law
… excerpt ends here. Continue reading the full article.
