An iron wire 2 km long and a copper wire 3 km long are connected in parallel across a source of voltage 200 V. Both wires carry the same current. The diameter of copper wire is 1 mm and its temperature is 100°C. Obtain the diameter of iron wire. The temperature coefficient of copper and iron at 20°C is 3.9 x 10-3 and 5 x 10-8 (°C)-1 respectively. Resistivity of copper and iron is 1.7 x 10-8 and 10-7 Ωm . Neglect the thermal conductivity of the wires.
