An electromagnet is a device that converts the flow of an electric current into a magnetic force. Unlike a permanent magnet, an electromagnet can be turned on and off.

The first hint that the flow of electricity created a magnetic field came in 1819 by the Danish physicist Hans Christian Oersted (1777-1851), who discovered that a compass needle was deflected when brought near a wire that had electricity flowing through it. (The same discovery was made almost 20 years earlier by the Italian Gian Domenico Romagnosi, but was completely ignored.) This unexpected discovery encouraged others, notably Michael Faraday and André Marie Ampère (1775-1836), to investigate further.

In 1820 English physicist William Sturgeon (1783-1850) built upon Oersted's discovery and Ampère's concept of the solenoid to invent the electromagnet. He took a soft-iron bar, wrapped it with eighteen turns of wire, and sent electricity through the wire. The...