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Physics · PYQ NEET UG 2025
हिन्दीThree 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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Correct answer · Option C
\( \frac{5}{3} \)
Explanation
Rate of heat flow is equal: \( \frac{2KA(3T - T_1)}{L} = \frac{KA(T_1 - T_2)}{L} = \frac{2KA(T_2 - T)}{L} \). Solving gives \( T_1 = \frac{7T}{3} \) and \( T_2 = \frac{5T}{3} \), hence \( T_1 / T_2 = 7/5 \) not directly listed, let's re-verify: equating resistances \( R_1 = L/(2KA), R_2 = L/(KA), R_3 = L/(2KA) \). Total resistance \( R = 2L/KA \). Temperature drops: \( \Delta T_1 = (R_1/R)(2T) = (1/4)(2T) = T/2 \implies T_1 = 3T - T/2 = 5T/2 \). Similarly \( T_2 = 3T/2 \). Thus \( T_1/T_2 = 5/3 \).
