Five rods of same dimensions are arranged as shown in the figure. They have thermal conductivities K1,K2,K3,K4 and K5. When points A and B are maintained at different temperatures, no heat flows through the central rod if
For no current flow between C and D
(Qt)AC=(Qt)CB⇒K1A(θA−θC)l=K2A(θC−θB)l
⇒θA−θCθC−θB=K2K1 ....(i)
Also (Qt)AD=(Qt)DB⇒K3A(θA−θD)l=K4A(θD−θB)l
⇒θA−θDθD−θB=K4K3 ....(ii)
It is given that θC=θD, hence from equation (i) and (ii) we get K2K1=K4K3⇒K1K4=K2K3