An inductor is a coil of wire that resists any change in current
Wind a wire into a coil and it gains a stubborn streak. Try to push more current through and it pushes back; try to cut the current and it fights to keep it flowing. That electrical inertia, stored in a magnetic field, lets inductors tune radios, smooth power and separate signals.
An inductor, also known as a coil, choke or reactor, is a simple two-terminal part, usually insulated wire wrapped in a helix. Current through it builds a magnetic field that holds energy. When the current changes, the shifting field induces a voltage in the wire, as Faraday's law describes, and Lenz's law says that voltage always pushes against the change. Rising current meets resistance as energy flows into the field; falling current is propped up as the field hands energy back.
The strength of this effect is called inductance, the ratio between the voltage produced and how fast the current is changing. Its unit is the henry, honouring the 19th-century American scientist Joseph Henry, and practical values run from about a millionth of a henry up to around 20. The name inductor seems to trace to Heinrich Ruhmkorff, who called the induction coil he built in 1851 an inductorium.
Geometry sets the value. Coiling the wire makes the magnetic field loop through the circuit many times, so more turns mean more inductance; spacing and shape matter too. Sliding a core of iron or ferrite inside helps enormously, because the material becomes magnetised and multiplies the flux, sometimes raising inductance several thousandfold.
Alongside resistors and capacitors, inductors form the trio of basic passive linear components. The capacitor is its mirror image, storing energy in an electric rather than a magnetic field. Inductors are especially common in alternating-current and radio gear. Built as chokes, they block AC while letting DC pass. In filters they sort signals by frequency, and paired with capacitors they create the tuned circuits that pick out a single station on a radio or television receiver.
Source: Inductor
