What does an inductor (coil) do in an electrical circuit?

An INDUCTOR (also called a coil or choke) is a coil of wire that stores energy in a magnetic field. KEY PROPERTY: Inductors OPPOSE CHANGES IN CURRENT (Lenz's Law) — this is called inductive reactance. When current increases: the magnetic field builds, inducing a back-EMF that opposes the increase; When current decreases: the collapsing field releases energy trying to maintain current. APPLICATIONS: Power supply filtering (smooths ripple); radio tuning circuits (with capacitors, forms LC resonant circuits); transformers (mutual inductance between coils); electric motors and generators. COMPARE with CAPACITOR: Capacitors oppose changes in VOLTAGE and store energy in an electric field; inductors oppose changes in CURRENT and store energy in a magnetic field.