14. 3 The equivalent Volume Current Density Je One molecule has a current with an area a, so its magnetic dipole moment is m= lae Consider a small length dl Taking dl as the hight and a cos o as the cross sectional area, we get a small volume adl cos o A molecule in this volume will contribute a current lad cos o all the molecules in this volume contribute a current Nadl cos0= Nm.dl=m. dl