4. Consider a neutral infinite sheet that lies in the xy-plane. The surface current K(+) = 0 for ± ≤0, but at t=0, suddenly the surface current turns on, so it is a constant Ko. In the +x direction, instantly, and every where in this plane. (No other charge density anywhere. I (9) Find the retarded scalar and vector potentials, VIF,+) and A(ft) everywhere in space. In computing your answer, Mote that E(r,t) (b) Find the Elf. +) and B (r, t) at a distance Z above (or below) the xy plane. Sketch these fields, and describe them. in words. Briefly comment on them and check whether it is what you would have expected from a static situation. (c) Show explicitly that B is not continuous at the xy plane, but that it satisfies the appropriate boundary condition there. Also, show explicitly that E also satisfies the appropriate boundary condition.