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# Inductor, inductance basics theory

An inductor is a coil of wire wound according to various designs, with or without a core of ferromagnetic material, to concentrate the magnetic flux resulting from current flowing in the wire.

Inductors provide us with a means of storing electrical energy in the form of a magnetic field. Typical applications of inductors include chokes, filters and frequency selective circuits (when is used in conjunction with one or more capacitors). The electrical characteristics of an inductor are determined by a number of factors including the material of the core , the number of turns, and the physical dimensions of the coil.

Inductance is the property of a coil which gives rise to the opposition to a change in the value of current flowing in it. A real coil comprises inductance (L) and a small resistance (R). Any change in the current applied to a coil/inductor will result in an induced voltage appearing across it.

Current flowing in a wire or coil produces a magnetic field around itself, and if the current suddenly stops, the magnetic field held out in space by the current will collapse back into the wire or coil. The measurement unit of inductance is henry (H) , 1H= 1W/1A (1 weber /1 ampere ). A coil have an inductance of 1H if a voltage of 1V is induced across it when a current changing at the rate of 1 A/s is flowing in it.

Because many of you don’t find useful a demonstration of a coil inductance we present now a few methods about how to calculate the inductance of a coil .

Series and Parallel Connection of Inductors

In order to obtain a particular value of inductance inductors may be connected in either series or parallel as shown below : For series connected inductors , the equivalent inductance will be equal with : L=L1+L2+…+Ln

,while for the parallel inductor connection the equivalent inductance of circuit is equal to the sum of the reciprocals of the individual inductance, like in this formula :

1/L= 1/L1 + 1/L2 + …+ 1/Ln .