# inductance

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## inductance,

quantity that measures the electromagnetic inductioninduction,
in electricity and magnetism, common name for three distinct phenomena. Electromagnetic induction is the production of an electromotive force (emf) in a conductor as a result of a changing magnetic field about the conductor and is the most important of the
of an electric circuit component; it is a property of the component itself rather than of the circuit as a whole. The self-inductance, L, of a circuit component determines the magnitude of the electromagnetic force (emf) induced in it as a result of a given rate of change of the current through the component. Similarly, the mutual inductance, M, of two components, one in each of two separate but closely located circuits, determines the emf that each may induce in the other for a given current change. Inductance is expressed in henrys [for Joseph HenryHenry, Joseph,
1797–1878, American physicist, b. Albany, N.Y., educated at Albany Academy. He taught (1826–32) mathematics and natural philosophy at Albany Academy and was professor of natural philosophy (1832–46) at Princeton (then the College of New Jersey).
]. An inductorinductor,
electric device consisting of one or more turns of wire and typically having two terminals. An inductor is usually connected into a circuit in order to raise the inductance to a desired value.
is a device designed to produce an inductance, e.g., a coil; an ideal inductor, i.e., one having no resistance or capacitance (see impedanceimpedance,
in electricity, measure in ohms of the degree to which an electric circuit resists the flow of electric current when a voltage is impressed across its terminals.
), is often called an inductance.

## Inductance

That property of an electric circuit or of two neighboring circuits whereby an electromotive force is induced (by the process of electromagnetic induction) in one of the circuits by a change of current in either of them. The term inductance coil is sometimes used as a synonym for inductor, a device possessing the property of inductance. See Electromagnetic induction, Electromotive force (emf), Inductor

For a given coil, the ratio of the electromotive force of induction to the rate of change of current in the coil is called the self-inductance of the coil. An alternative definition of self-inductance is the number of flux linkages per unit current. Flux linkage is the product of the flux and the number of turns in the coil. Self-inductance does not affect a circuit in which the current is unchanging; however, it is of great importance when there is a changing current, since there is an induced emf during the time that the change takes place. For example, in an alternating-current circuit, the current is constantly changing and the inductance is an important factor.

The mutual inductance of two neighboring circuits is defined as the ratio of the emf induced in one circuit to the rate of change of current in the other circuit.

The International System (SI) unit of mutual inductance is the henry, the same as the unit of self-inductance. The same value is obtained for a pair of coils, regardless of which coil is the starting point.

The mutual inductance of two circuits may also be expressed as the ratio of the flux linkages produced in a circuit by the current in a second circuit to the current in the second circuit. See Inductance measurement

## Inductance

a physical quantity that characterizes the magnetic properties of an electric circuit. Current flowing through a conductive circuit generates a magnetic field in the surrounding space. The magnetic flux Φ permeating the circuit (coupled with the circuit) is directly proportional to the current intensity I:

(1) ϕ = LI

The proportionality constant L is called the inductance or self-inductance of the circuit.

Inductance depends on the dimensions and shape of the circuit and also on the magnetic permeability of the surrounding medium. In the International System of Units (SI), inductance is measured in henrys (H); in the cgs (Gauss) system it has the dimension of length, and therefore the unit of inductance is called the centimeter (1 H = 109 cm).

The self-induced electromotive force in a circuit that arises upon a change in current is expressed through inductance:

(2) E = -LIt)

(where Δ I is the change in current over time Δ t). For a given current intensity, inductance determines the energy W of the magnetic field of the current:

(3) W = (LI2)/2

The greater the inductance, the greater the magnetic energy that is accumulated in the space surrounding the current-carrying circuit. Drawing an analogy between electrical and mechanical phenomena, magnetic energy is similar to the kinetic energy of a body T= mv2/2 (where m is the mass of the body and v is the velocity of its motion). In this case, inductance corresponds to mass and current corresponds to velocity. Thus, inductance determines the inertial properties of current.

In practice, the parts of a circuit that have considerable inductance are made as inductance coils. To increase L, coils with iron cores are used. However, since the magnetic permeability μ of ferromagnets depends on field intensity and, therefore, on the current intensity, inductance becomes dependent on I. The inductance of a long solenoid with N turns, cross-sectional area S, and length l, in a medium with magnetic permeability μ., is (in SI units) L = μμ0N2S/l, where μ0 is the magnetic constant, or the magnetic permeability of a vacuum.

### REFERENCE

Kalashnikov, S. G. Elektrichestvo. Moscow, 1970. Chapter 9. ’Obshchiikurs fiziki, vol. 2.)

G. IA. MIAKISHEV

## inductance

[in′dək·təns]
(electromagnetism)
That property of an electric circuit or of two neighboring circuits whereby an electromotive force is generated (by the process of electromagnetic induction) in one circuit by a change of current in itself or in the other.
Quantitatively, the ratio of the emf (electromotive force) to the rate of change of the current.
(control systems)

## inductance

1. the property of an electric circuit as a result of which an electromotive force is created by a change of current in the same circuit (see self-inductance) or in a neighbouring circuit (see mutual inductance). It is usually measured in henries.
2. another name for inductor

## inductance

The magnetic field that is generated when a current is passed through an inductor, typically a wire coil. Inductance is measured in henrys (H). See inductor and induction.
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