A cylinder of radius r made of a material of thermal conductivity `K_(1) = K` is surrounded bt cylendrical shell of inner radius R and outer radius 3R made of a material of thermal conductivity `K_(2) = 2K`. The two ends of the combined system are maintained at two different temperatures .
there is no loss of heat across the cylendrical surface and system is in steadt state . what is the effective thermal conductivity of the system ?