Electromagnet

An electromagnet is a magnet whose magnetic field is produced by electric current, usually flowing through a coil. Its strength can be controlled by changing the current or the coil’s design.

Ampère's circuital law: A law relating the magnetic field integrated around a closed path to the electric current passing through it. It connects current in the coil to the magnetic field circulating around the windings.
Electric current: The rate at which electric charge flows through a conductor or other medium. Current through the winding is the source of an electromagnet’s magnetic field.
Relay: An electrically operated switch that uses an electromagnet to move one or more contacts. A relay uses coil current to control a separate electrical circuit.
Hans Christian Ørsted: A Danish physicist who discovered in 1820 that an electric current deflects a magnetic compass needle. His observation established that electric currents produce magnetic effects.
Permanent magnet: An object that produces a persistent magnetic field without requiring a continuous electric current. Unlike a permanent magnet, an electromagnet can be switched off and adjusted electrically.
Solenoid: A helical coil of wire that produces a magnetic field when electric current flows through it. A long solenoid is the standard geometry for a nearly uniform electromagnet field.
Magnetic field: A vector field that describes magnetic forces on moving charges, currents, and magnetic materials. An electromagnet is defined by the magnetic field its current creates.
Solenoid valve: A valve operated by an electromagnetic coil that moves a plunger or armature. Its electromagnet converts an electrical signal into fluid-flow control.
William Sturgeon: An English physicist who built a practical iron-core electromagnet in 1825. His device demonstrated how a coil and iron core could make a powerful switchable magnet.
Electret: A material that retains a persistent electric polarization after an external electric field is removed. It is an electrostatic analogue of a permanent magnet, not a device driven by coil current.

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