An electric cable, 8 mm in diameter is covered by plastic sheathing (k = 0.18 W/m.K). The surface temperature of cable was observed as 50°C when it is exposed to air at 20°C with convective...

An electric cable, 8 mm in diameter is covered by plastic sheathing (k = 0.18 W/m.K). The surface temperature of cable was observed as 50°C when it is exposed to air at 20°C with convective coefficient of 12.0 W/m².K. Calculate :

 (i) the thickness of insulation to keep the wire as cool as possible, and

 (ii) surface temperature of insulated cable, if the intensity of current flowing the conductor remains unchanged.