Electromagnet

Lore & Background

Danish scientist Hans Christian Ørsted discovered in 1820 that electric currents create magnetic fields. In the same year, French scientist André-Marie Ampère showed that iron can be magnetized by inserting it into an electrically fed solenoid. Sturgeon's magnet weighed seven ounces but could lift nine pounds when current from a single-cell power supply was applied. However, his magnets were weak because uninsulated wire could only be wrapped in a single spaced-out layer. The first major use for electromagnets was in telegraph sounders.

Reader's Guide

Electromagnets are fundamental to modern technology, serving as components in motors, generators, transformers, relays, loudspeakers, hard disks, MRI machines, and magnetic separation equipment. They are also employed in industry for lifting heavy iron objects. The ability to control the magnetic field by varying the electric current makes them versatile, unlike permanent magnets that require no power. The physics relies on Ampere's law: an electric current in a wire creates a magnetic field, concentrated by winding the wire into a coil. The direction of the field is given by the right-hand rule. A common tractive electromagnet is a solenoid with a plunger; the force depends on factors such as cross-sectional area, number of turns, current, and solenoid length. Improvements like conical ends and magnetic return paths enhance performance. The historical development from Sturgeon's simple horseshoe magnet to Henry's layered coils enabled practical applications, and later quantum theory explained ferromagnetic behavior.

Did You Know?

• William Sturgeon's first electromagnet weighed seven ounces but could lift nine pounds.
• Joseph Henry used silk-thread-insulated wire to wind multiple layers, creating magnets that could support over 2,000 pounds.
• The magnetic field of an electromagnet disappears when the current is turned off.
• The first major use for electromagnets was in telegraph sounders.