Lifting electromagnets have many advantages: the presence or absence of the magnetism of the lifting electromagnet can be controlled by on/off current; the magnitude of the magnet can be controlled by the strength of the current or the number of turns of the coil; it can also be controlled by changing the magnitude of the resistance control current. Magnetic size; its magnetic pole can be controlled by changing the direction of the current, and so on. That is, the strength of the magnetic force can be changed, the presence or absence of the magnetic force can be controlled, and the direction of the magnetic pole can be changed.
History of electromagnets In 1822, the French physicists Arago and Lussac discovered that when current was passed through a winding of iron, it could magnetize the iron in the winding. This is actually the initial discovery of the electromagnet principle. In 1823, Sturgeon did a similar experiment: he wrapped 18 turns of bare copper wire on a U-shaped iron bar that was not a magnet bar. When the copper wire was connected to the voltaic cell, it was wound around U. The copper coil on the iron rod creates a dense magnetic field, which turns the U-shaped iron rod into an "electromagnet". The magnetic energy on this electromagnet is many times larger than that of the permanent magnet. It can suck up the iron block 20 times heavier. When the power is cut off, the U-shaped iron bar can not attract any iron block. Root ordinary iron rod.