The result of magnetization is equivalent to a current on the surface of the material,called an amperian current(表面电流) Density ofAmperian current Amperian current per unit length △V J,The result of magnetization is equivalent to a current on the surface of the material, called an amperian current（表面电流） Density of Amperian current Is l M s m s j lS j lS V p M        Amperian current per unit length