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20/09/2020 4:28 pm
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The rods of identical cross-section and lengths are made of three different materials of thermal conductivity K1, K2 and K3, respectively. They are joined together at their ends to make a long rod (see figure). One end for the long rod is maintained at 100ºC and the other at 0ºC (see figure). If the joints of the rod are at 70ºC and 20ºC in steady state and there is no loss of energy from the surface of the rod, the correct relationship between K1, K2 and K3 is :
(1) K1 < K2 < K3
(2) K1 : K3 = 2 : 3
(3) K1 : K2 = 5 : 2
(4) K1 > K2 > K3
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20/09/2020 4:40 pm
(2) K1 : K3 = 2 : 3
Explanation:
K1 : K3 (100 – 70) = K2(70 – 20) = K3(20 – 0)
K130 = K2(50) = K3(20)
=> K1 : K3 : K2 : K3 = 10 : 6 : 15
K1 : K3 = 2 : 3