Two different metal rods of the same length their ends kept at the same temperatures θ1 and θ2 with θ2 > θ1 If A1 and A2 are their cross-sectional area and K1 and K2 their thermal conductivities, the rate of flow of heat in the two rods will be the same if
A1A2 =K2K1
Rate of flow is QT=KA(θ1−θ2)l Since (θ1−θ2) and l are the same for the two rods, the rate of flow QT will be the same if the product KA is the same for the two rods,i.e. if k1A1=K2A2 or A1A2=K2K1 Hence the correct choice is (b)