William Sturgeon demonstrated an electromagnet in 1825 using a coil of wire around an iron core.
An electromagnet produces a magnetic field when electric current flows through its coil. The iron core strengthens the field because it becomes magnetized by the current and loses most of that magnetism when the current stops.
Sturgeon’s design was an important early improvement in electromagnetism. Earlier experiments had shown links between electricity and magnetism, but his device could lift considerably more iron than the bare conducting wire alone. This made electromagnets useful for later telegraphy, electrical instruments, relays, and motors.
An electromagnet differs from a permanent magnet because its magnetism is controlled by current. Increasing the number of coil turns or the current generally strengthens the magnetic field, although heating and the core material limit practical performance. Sturgeon’s 1825 demonstration predates the development of many familiar electrical machines.