Inductance is introduced intentionally in circuits for various purposes, some of which are described in the sequel. In most applications where either inductance or capacitance could be used, such as in active filters and integrating and differentiating circuits, capacitance is preferred because of the smaller size and lower cost of capacitors, relative to inductors. Also, it is easier to confine the electric field in a capacitor than it is to confine the magnetic field produced by an inductor, so capacitors produce less electrical interference than inductors.

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Inductance the characteristics of an electrical conductor that opposes a change in current flow. The symbol for inductance is L. An inductor is a device that stores energy in a magnetic field. Inductance exhibits the same effect on current in an electric circuit as inertia does on velocity of a mechanical object. It takes more work to start a load moving than it does to keep it moving because the load possesses the property of inertia. Inertia is the characteristics of mass that opposes a change in velocity. Once current is moving though a conductor, inductance helps to keep it moving. The effects of inductance helps to keep it moving. The effects of inductance are sometimes desirable and other times undesirable.

The property of one coil due to which it opposes the change of current in the other coil is called mutual inductance between the two coils. This property is attained by a coil due to mutually induced emf in the coil, while current in the neighbouring coil is changing.

An inductor is a device that can store energy in a magnetic field. Coils, solenoids and toroids are all examples of inductors. For practical inductors, however, nonideal effects may alter this voltage-current relationship through an additional series resistance and possible lead capacitance and inductance. Assuming an ideal inductor, the computation of inductance becomes a strictly magnetostatic problem. Considering one or more loops of current in space, it can be shown that the magnetic flux through a loop is proportional to the current that produces the magnetic flux. The constant of proportionality is called inductance with units of henry (H). Specifically, inductance is defined in terms of the flux linkage and current as:

$L_{ij}$ = $\frac{Flux\ linkage\ through\ ith\ coil\ due\ to\ current\ in\ jth\ coil}{Current\ in\ jth\ coil}$

The unit by which inductance is measured is the Henry (H), named for Joseph Henry (1797-1878), an American physicist. A Henry is the amount of inductance required to induce an emf of 1 volt when the current in a conductor changes at the rate of 1 ampere per second. The Henry is a large unit; the millihenry (mH) and microhenry (\muH) are more commonly used.

In a coil, the inductive action is multiplied because the lines of magnetic flux emanating from one section of the coil not only cut through the wire from which they originate, but they also cut through the sections of the coil adjacent to it. The more wire that is present, the more the opposition will be to any changes in current within that wire. Thus, the number of turns of wire determines a coil's inductance value. The magnetic field of a coil is like the magnetic field of a bar magnet.

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