<P> The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be quickly changed by controlling the amount of electric current in the winding . However, unlike a permanent magnet that needs no power, an electromagnet requires a continuous supply of current to maintain the magnetic field . </P> <P> Electromagnets are widely used as components of other electrical devices, such as motors, generators, electromechanical solenoids, relays, loudspeakers, hard disks, MRI machines, scientific instruments, and magnetic separation equipment . Electromagnets are also employed in industry for picking up and moving heavy iron objects such as scrap iron and steel . </P> <P> Danish scientist Hans Christian Ørsted discovered in 1820 that electric currents create magnetic fields . British scientist William Sturgeon invented the electromagnet in 1824 . His first electromagnet was a horseshoe - shaped piece of iron that was wrapped with about 18 turns of bare copper wire (insulated wire didn't exist yet). The iron was varnished to insulate it from the windings . When a current was passed through the coil, the iron became magnetized and attracted other pieces of iron; when the current was stopped, it lost magnetization . Sturgeon displayed its power by showing that although it only weighed seven ounces (roughly 200 grams), it could lift nine pounds (roughly 4 kilos) when the current of a single - cell battery was applied . However, Sturgeon's magnets were weak because the uninsulated wire he used could only be wrapped in a single spaced out layer around the core, limiting the number of turns . </P> <P> Beginning in 1830, US scientist Joseph Henry systematically improved and popularized the electromagnet . By using wire insulated by silk thread, and inspired by Schweigger's use of multiple turns of wire to make a galvanometer, he was able to wind multiple layers of wire on cores, creating powerful magnets with thousands of turns of wire, including one that could support 2,063 lb (936 kg). The first major use for electromagnets was in telegraph sounders . </P>

What kind of wire is used in electromagnets