Three identical heat conducting rods are connected in series as shown… | NEET 2025

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Heat Conduction

Three identical heat conducting rods are connected in series as shown in the figure. The rods on the sides have thermal conductivity $2K$ while that in the middle has thermal conductivity $K$ . The left end of the combination is maintained at temperature $3T$ and the right end at $T$ . The rods are thermally insulated from outside. In steady state, temperature at the left junction is $T_1$ and that at the right junction is $T_2$ . The ratio $T_1/T_2$ is

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Answer: (a)

$R = \frac{L}{KA}$ : the $2K$ rods have resistance $r$ , the middle $K$ rod has $2r$ ; total $4r$ .
Total drop $3T - T = 2T$ , so the drop per $r$ is $\frac{T}{2}$ .
$T_1 = 3T - \frac{T}{2} = \frac{5T}{2}$ , $T_2 = \frac{5T}{2} - T = \frac{3T}{2}$
$\frac{T_1}{T_2} = \frac{5}{3}$ , so the answer is (a).

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