Practice question

**Magnetic field lines** form continuous closed loops, direction given by tangent at point, density indicates field strength. Unlike electric field lines, magnetic lines never intersect because unique field direction exists at each point, and bar magnet possesses dipole moment m = N I A directed from south to north pole inside magnet. Magnetic field lines form continuous closed loops because there are no magnetic monopoles; they emerge from the north pole and enter the south pole, looping back internally. In contrast, electric field lines of a dipole start at the positive charge and end at the negative charge, or extend to infinity if unterminated. Substituting