11.4.2 Interface Conditions for the Magnetic Field
An almost identical sequence follows for the evaluation of the interface conditions for the magnetic field. The same interface
between two general materials as in Figure 11.2a is used except that now, because we use Ampere’s law, there are no charge
densities on the interface but, rather, a current density. The conditions for application of Ampere’s law are shown in
Figure 11.2b. The following conditions are used:
(1) The contour abcda encloses the interface alone; that is, bc and da tend to zero and the area of the contour tends to zero.
(2) The tangential component of the magnetic field intensity in material (1) is in the same direction as the direction of
integration, whereas in material (2), it is in the opposite direction.
(3) The total current enclosed by the contour is equal to the (surface) current density on the surface multiplied by the length
ab (or cd, since these may be taken to be equal).