To answer this question that is often asked by readers, it is necessary to explain first of all what is the difference between magnet from non-magnetic steel bar. Each atom of iron in the composition of the steel is magnetized or unmagnetized, we can imagine how small magnet. In unmagnetized steel atomic magnets are arranged randomly so that each is destroyed by the opposite action of the set back of the magnet (Fig. 1, a). On the contrary, in the magnet all the elementary magnets are ordered, the same poles in the same direction, as shown in Fig. 1, b.
Fig. 1. a - the location of the atomic magnets in the unmagnetized bar steel; b - the same in magnetized steel; in - action pole of the magnet on the atomic magnets magnetized steel.
What happens in a piece of steel when it is rubbed with a magnet? By the power of his attraction magnet rotates elementary steel bar magnets with similar poles in the same direction. Fig. 1, b shows how this happens: the elementary magnets are rotated first South pole to the North pole of the magnet, and then, when the magnet is given hereinafter, are arranged along the direction of its movement, the South poles to the middle of the bar.
It's easy to understand how to operate a magnet for magnetization of the bar steel: needs to be attached to the end of the bar one pole of the magnet and, pressing firmly, keep a magnet along the bar. This is one of the simplest and oldest methods of magnetization, valid, however, only a weak magnets are small in size. Strong magnets can be constructed using the properties of the electric current.