Remarks 1. This is called Ampere's circuital law, and only free current is involved in this equation 2. In practice it is difficult to give the equivalent current Ie. By using this Amperes circuital law, one calculate the magnetic field intensity h without nowin ng le 3. Outside the magnetic material the ampere' s cir- cuital law reduces to the old ampere 's circuital law B·dl=p0l 4. The term sch. dl is called the magnetomotance