Rods x and y of equal dimensions but of different materials are joined as shown in figure. Temperatures of end points A and F are maintained at 100 and 40 respectively. Given the thermal conductivity of rod x is three times of that of rod y, the temperature at junction points B and E are (close to): (a) 60 and 45 respectively (b) 80 and 70 respectively (c) 89 and 73 respectively (d) 80 and 60 respectively

Answer: (c). A 100°CBEF 40°Cr3r3rrr3r Kx = 3Ky, so take resistance of an x rod = r and a y rod = 3r. B to E: path BCE = 6r in parallel with path BDE = 2r, giving (6 × 2)/(8)r = 1.5r. Total = r + 1.5r + 3r = 5.5r; current H = (60)/(5.5r) ≈ 10.9/r TB = 100 - 10.9 ≈ 89, TE = 40 + 3(10.9) ≈ 73 So the answer is (c).

Rods x and y of equal dimensions but of different materials are… | JEE Main 2026 (22 Jan, Shift 1)

Q10JEE Main 2026 · 22 JAN · SHIFT 1Medium

Heat Conduction

Rods $x$ and $y$ of equal dimensions but of different materials are joined as shown in figure. Temperatures of end points $A$ and $F$ are maintained at $100^\circ\text{C}$ and $40^\circ\text{C}$ respectively. Given the thermal conductivity of $\text{rod } x$ is three times of that of $\text{rod } y$ , the temperature at junction points $B$ and $E$ are (close to):

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Answer: (c)

$K_x = 3K_y$ , so take resistance of an $x$ rod $= r$ and a $y$ rod $= 3r$ .
B to E: path BCE $= 6r$ in parallel with path BDE $= 2r$ , giving $\frac{6 \times 2}{8}r = 1.5r$ .
Total $= r + 1.5r + 3r = 5.5r$ ; current $H = \frac{60}{5.5r} \approx \frac{10.9}{r}$
$T_B = 100 - 10.9 \approx 89^\circ\text{C}$ , $T_E = 40 + 3(10.9) \approx 73^\circ\text{C}$
So the answer is (c).

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Heat Conduction question from JEE Main 2026 (22 Jan, Shift 1)

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