Each square cell has a cross-sectional area a" and 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 le surface curre ent density a=M Thus, taking into account of the direction, one gets le= M X n1 called the equivalent surface current density Recall the bound surface charge density ob=Pn