a magnet with an on-off switch, powered by electricity's habit of making tiny compasses spin.
means a coil of wire that becomes magnetic only when electric current flows through it, and stops when the current stops.
from discovered in 1820 when hans christian oersted noticed a compass needle twitch near a live wire, proving electricity and magnetism were the same force wearing different hats; william sturgeon built the first practical one in 1824 by wrapping wire around an iron bar.
mri scanners — use superconducting electromagnets near 1.5 to 3 tesla for imaging
maglev trains — japan's l0 series floats at 603 km/h using them
junkyard cranes — lift entire cars then drop them by cutting current
large hadron collider — steers particles with magnets cooled to -271 celsius