Two cylindrical rods, one copper and the other iron, are identical in lengths and cross-sectional areas. They are joined end to end to form one long rod. A 12-V battery is connected across the free ends of the copper-iron rod. What is the voltage between the ends of the copper rod? Resistivities of copper and iron are respectively: 1.72*10^-8 ohm m and 9.7*10^-8 ohm m.