The use of instantaneous point sources or Green's functions in evaluating electromagnetic fields

IN a previous paper1 it was shown how expressions for vector potential could be derived from corresponding values of scalar potential for a point source; these expressions are given in the author's Tables of Green's Functions.2 It was then shown how these vector-potential expressions could be used to derive the fields due to uniformly magnetized disks, or due to coils, building them up from magnetic doublets or individual current elements by integration. The examples given in that paper1 were limited to those in which the field did not vary with time, since some additional concepts need to be introduced when the field varies with time. These will be considered here, and examples given of the field due to conductors or coils in which the current varies with time.