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This is defined1 as "a device, the primary purpose of which is to introduce inductance into an electric circuit." There are self inductors and mutual inductors, but the dual wording is seldom used. An equivalent circuit of an inductor is shown in Fig. 3. The resistance shown is the effective resistance, and the capacitance is the distributed capacitance between turns. Inductors are often called inductance coils, choke coils, or merely coils and chokes.

equivalent circuit of an inductor
Figure 3. An equivalent circuit of an inductor. The capacitance and resistance are undesired.

Inductors used in communication are of two general types, those using air cores, and those using ferromagnetic cores, such as silicon steel laminations. For very low frequencies and where the core losses (eddy-current and magnetic hysteresis losses) are not of extreme importance, cores of silicon steel are used. When the losses must be kept to the minimum and high-quality performance is desired, cores of compressed powdered Permalloy are employed. As explained on page 52, the core losses will become very great at radio frequencies, and for this reason air cores are often used. There is a growing tendency, however, to use cores of compressed powdered ferromagnetic material such as iron at radio frequencies.

What is called the energy storage factor Q of an inductor is usually defined as the ratio of the energy stored to the energy dissipated per cycle. Numerically,

This is the ratio of the inductive reactance of a coil to its resistance.

Last Update: 2011-05-30