The temperature drop through a two layer furnace wall is 900°C. Each layer is of equal area of cross section. Which of the following actions will definitely result in lowering the temperature θ of the interface?

Net resistance of two wall=  l1k1+l2k21ATemperature of interface =  θ=1000−ΔTl1k1+l2k2×l1k1…..(1)On increasing thermal conductivity of outer layer k2 , temp of interface certainly decreases.or  θ=ΔTl1k1+l2k2×l2k2+100………..(2)On increasing thickness of Inner layer l1 temperature of interface decreases.