A long copper rod of 3cm diameter conducts a current of 1000 ampere and has an electrical resistance of 20 x 106 ohm per meter length. The rod is insulated to radius of 1.8 cm with fibrous cotton having a thermal conductivity of ke = 0.06 W/m-deg. Which is further covered by a plastic cover of thermal conductivity of Kp = 0.4 W/m-deg. The surrounding are at temperature of 25C and heat transfer coefficient between plastic and surrounding is 10W/m -deg. Find out the thickness of the layer of plastic which gives the minimum temperature in cotton insulation for this condition, Find the temperature of copper and max. temp. in plastic layer.