Each square cell has a cross-sectional area an a length l, and carries a surface current density a (ampere per meter) Each cell has a magnetic moment m= ala Each cell has a magnetization M=m/volume= a Inside all the currents cancel except at the bound ary with the surface current density a=M Thus, taking into account of the direction, one gets e M×n 1 called the equivalent surface current densi Recall the bound surface charge density Ob=Pn