electromagnet

An electromagnet is a magnet in which the magnetic field is produced by an electric current. It typically consists of a coil of insulated wire wrapped around a ferromagnetic core, such as soft iron. When current flows through the coil, a magnetic field is generated; the iron core concentrates and intensifies the field, allowing the device to exert magnetic force. The magnet can be switched on and off by controlling the current, and the polarity follows the direction of current according to the right-hand rule.

Construction and operation: The core is often laminated to reduce energy losses from eddy currents, especially in alternating-current applications. The strength of the field is proportional to the current and to the number of turns in the coil. Increasing either increases magnetism; a high-permeability core increases flux. In AC or rapidly changing conditions, impedance, frequency response, and core geometry influence performance.

Types and examples: DC electromagnets produce a steady field and are common in lifting devices, relays, and solenoids. Solenoids are cylindrical coils that can move a ferromagnetic plunger; they are widely used in valves and actuators. Electromagnets designed for alternating current or pulsed operation are used in switching, braking, and timing devices.

History and significance: The concept arose from 19th-century studies of electricity and magnetism. William Sturgeon built the first practical electromagnet in the 1820s, enabling controllable magnetic forces. The development of electromagnets helped lead to electrical relays, transformers, and many electromechanical devices.

Applications and limitations: Electromagnets are used for lifting heavy metallic loads, in relays and switches, door locks, magnetic separation, and scientific instrumentation. Limitations include power consumption, heat generation, and magnetic saturation, which constrain performance at high current levels.