A current of 1000 A is flowing through a long copper conductor (K-390 W/m.K), 25 mm in diameter, that has on electric resistivity of 1.08 μΩ cm. This rod is insulate to a radius of 17.5 mm with fibrous cotton (K = 0.058 W/m.K), which is further covered by a layer of plastic (K = 0.42 W/m.K). It is then exposed to the surrounding air at 20°C with a heat transfer coefficient of 20.5 W/m ² K. Calculate the (i) Thickness of the plastic layer that gives the minimum temperance in a cotton insulation, (ii) Temperature of the copper rod and the maximum temperature in the plastic layer for the condition described.