A coil, inductor, or choke is a passive electrical component that stores energy in its magnetic field. The primary form of coils consists of a wire wound around a metallic core, usually shaped like a cylinder or disk. When current flows through the coil, its magnetic field is created and the stored energy increases proportionally to the current. Inductors are used to create an inductive reactance in an LC circuit where capacitive reactance is present. This causes the reactance to oppose changes in current and can be used to filter the currents. Chokes consist of several turns of insulated wire wound around a single core or multiple cores that can be used to reduce AC ripple or oscillations in power circuits. They are also used to filter or reduce the amplitude of alternating current signals. Coils are used for a variety of applications, including transformers, motors, generators, and antennas.