複選題7. Which are correct with the Poynting vector ? (A) is the energy per unit area and per unit time, transported by the electromagnetic fields. (B) is the electromagnetic force per unit area acting on a surface. (C) /c2 is the momentum current density transported by the fields. (D) /c2 is the momentum per unit volume stored in the electromagnetic fields. (E) /c2 is the work done on the charges by the electromagnetic force.