inductor

inductor, 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. Since inductance is a property that varies with frequency, inductors range from a single loop in a length of wire (used at ultrahigh frequencies), through spirals in the copper coating of an etched circuit board (used at very high frequencies), to large coils of insulated wire wound onto iron or ferrite cores. For radio use, inductors often have air cores to avoid the losses caused by magnetic hysteresis and by eddy currents that occur when solid cores are used. Solid cores, however, offer the advantage of raising the inductance that can be obtained from a coil of a given number of turns of wire. Ferrites are often used, since they are nonconductors and are immune to eddy currents.

---

A coil of wire that generates a magnetic field when current is passed through it. The strength of the magnetic field is measured in henrys (H). When the current is removed, as the magnetic field disintegrates, it "induces" a brief current in the opposite direction of the original. Thus "induction" is caused by the opening and closing of a DC circuit or the continuous changing of directions in an AC circuit.

High-Frequency Filters
An induction coil impedes the flow of high-frequencies in an AC circuit, which is why inductors are used as surge protectors, choking off any high-frequency shifts. The tiny donuts placed on the end of signal cables and the load coils placed into telephone networks are examples. See induction.