Displacement field ed iv. superposition of sources for the displacement field in systems containing dielectrics, we often consider any field caused by the dielectric as an induced field, and any other field as an external field. a. consider the electrostatic field. 1. is the electrostatic field sourced by free charges, bound charges, or both? 2. suppose you wanted to determine the net electric field by superposition. what would be the most convenient way to subdivide net electric field? write out the divergence and curl for each portion of the net electric field. now consider the displacement field. b. 1. would a displacement field sourced only by free charges be considered an external field or an induced field? would this field be sourced by curl only, by divergence only, or by both? would the induced displacement field due to the polarization be sourced by curl only, by divergence only, or by both? 2. the net displacement field can be thought of as a sum of these two fields: dnt =dext +dnd is this definition of d. t consistent with v .d = piree? (hint: does one term have no divergence? )