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The initial discovery of magnetic phenomenon
In 1822, the French physicist- Arago and Gay-Lussac found that when the current passes the winding with iron, which enables the winding iron magnetized. This is actually the initial discovery of the principle of the electromagnet.
In 1823, Sturgeon also done a similar experiment: he winded around 18 laps of copper bare wire on U-shaped iron bar that is not a magnet bar. When the copper wire and the voltaic battery are switched on, the copper coils around in a U-shaped iron bar will produce the dense magnetic field, which makes U type iron bar into a" magnet". The magnetic energy on the electro-magnet is larger times than the permanent magnet’s., It can pick up the iron that is 20 times heavier than if. When power supply is cut off, the iron bar of U type can not absorb any iron, which becomes a common iron bar.
from：http://www.htmagnets.com/newsd-nid-7.html
