The magnets for us is a "magic" of our childhood, a childhood memory. But you know the magnet is not invented, is a natural magnetite. Ancient Chinese discovered a kind of natural magnetized stone in nature, calling it "magnetite." This stone can magically suck up a small piece of iron, and always swing in the same direction.
In 1822, French physicists Arago and Lussac found that when a current was passed through a wire wound in it, it could magnetize the iron in the wire. This is actually the original discovery of the electromagnet principle. In 1823, Strkin also did a similar experiment: he wound 18 turns of bare copper wire on a U-bar that was not a magnet bar. When the copper wire was connected to a voltaic cell, it wound around U The copper coil on the iron rod creates a dense magnetic field that turns the U-bar into an "electromagnet." The magnetic energy on this electromagnet can be magnified many times than that of permanent magnet, it can suck the iron 20 times heavier than it, and when the power is cut off, the U-shaped iron can not absorb any iron, Ordinary iron bars.