A3-mm-diameter electrical wire is insulated by a 2-mm-thick rubberized sheath (k = 0.13 w/m ⋅ k), and the wire/sheath interface is characterized by a thermal contact resistance of rt ,c 3 10 m k/w ′′ = × −4 2 ⋅ . the convection heat transfer coefficient at the outer surface of the sheath is 15 w/m2 ⋅ k, and the temperature of the ambient air is 20°c. if the temperature of the insulation may not exceed 50°c, what is the maximum allowable electrical power that may be dissipated per unit length of the conductor? what is the critical radius of the insulation?