A wire, in which electric current passes (electrons in motion), generates a magnetic field in its vicinity. The intensity of the magnetic field depends on the intensity of the current and the shape of the wire. In principle, each wire crossed by an electric current is an electromagnet. Usually in the electromagnets a soft iron core is inserted inside the coil because this considerably increases its magnetic field. This happens because the magnetic field in the coil polarizes the soft iron core, making it in turn become a magnet. The core in soft iron, at the moment when no more current passes, loses its magnetization. This is wanted, because it allows to turn on and off the magnet.