One end of a rod of length `20cm` is inserted in a furnace at `800K` The sides of the rod are coverd with an insulating meterial and the other end emits radiation like a black boy The temperature of this end is `750K` in the steady state The temperature of the surrounding air is `300K` Assuming radiation to be the only imporatant mode of energy transfer between the surrounding and the open end of the rod, find the thermal conductivity of the rod Stefan's constant `sigma = 6.0 xx 10^(8) W m^(-2) K^(-4)` .