Throughout a region, equipotential surfaces are given by z=constant. The surfaces are equally spaced with V=100V for z=0.00m, V=200V for z=0.50m, V=300V for z=1.00m. What is the electric field in this region? 100 V/m in the -z direction 400 V/m in the -z direction 200 V/m in the -z direction 300 V/m in the -z direction