I understood that curl H = J H being magnetic field intensity and magnetic flux density B = u H (u being permeability of free space) divergence of B is zero because isolated magnetic charge or pole doesn't exist. but then they define magnetic scalar and vector potentials .i can imagine H and B like in terms of field lines but this scalar and vector potentials making me very uncomfortable. They say H= - del Vm (negative divergence of scalar potential) and this is valid only when current density J=0. What i undertood is, first of all static magnetic field is produced by constant current if current density is zero which is del I / del S then current is zero then how can magnetic field exist at first place. And then they define magnetic vector potential (A) exist just because del . B =0(div of B =0) so B can be expressed as curl of some function since divergence of curl of a vector is zero . I understand this in terms of vector identities but m not able to imagine this magnetic vector potential. Some body please explain this. Any link to a simulation or java applet will be very helpfull . . . Thank u.