has been called "the law of nonexistence of isolated monopoles," among others. We prefer the last of the three cited name because it reminds us of the parallelism, as well as the differences,between the electric and magnetic laws of nature.
The difference between Gauss's law for electricity and its magnetic counterpart can be elucidated in terms of field lines. Electric field lines originate from positive electric charges and terminate on nagative ones. Hence,for the electric field lines of the electric dipole shown in Fig. 5-15(a),the electric flux through a closed surface surrounding one of the charges is nonzero. In contrast, magnetic field lines always form continuous closed loops. As we saw in Section 5-2, the magnetic field lines due to currents do not begin or end at any point; this ie true for the linear conductor of Fig. 5-11 and the circular loop of Fig. 5-12, as well as for any current distribution. It is also true for a bar magnet [Fig. 5-15(b)]. Because the magnetic field lines form closed loops, the net magnetic flux through any closed surface surrounding the south pole of the magnet (or thought any other closed surface) is always zero, regardless of its shape.