Copper and aluminum are being considered for a high-voltage transmission line that must carry a current of 62.1 a. the resistance per unit length is to be 0.153 0/km. the densities of copper and aluminum are 8960 and 2600 kg/m, respectively. compute(a) the magnitude of the current density and (b) the mass per unit length a for a copper cable and (c) and (d) for an aluminum cable. (a) number units (b) number units (c) number units units (d) number