Magnetic field. Computer artwork of the magnetic field around a magnet. The field is the three- dimensional region around a magnet where magnetic forces can be experienced. It is represented here as a series of lines which run in closed loops between the poles of the magnet (red and green). A magnetic field always runs from the north pole to the south pole. The field lines show the path that a magnetic north pole would follow if placed within the field. The magnetic forces which cause the pole to move are produced by the motion of charged particles within the magnet. The strength of the magnetic field decreases as the distance from the magnet increases.