Solved: PHYSICS Question for NEET

NEET PHYSICSMedium

Two rods $A$ and $B$ of different materials are welded together as shown in the figure. Their thermal conductivities are $K_1$ and $K_2$ . The thermal conductivity of the composite rod will be:

$\frac{3(K_1+K_2)}{2}$

$K_1+K_2$

$2(K_1+K_2)$

$\frac{K_1+K_2}{2}$

Step-by-Step Solution

Assuming the two rods are welded in a parallel combination and have the same dimensions (length $L$ and cross-sectional area $A$ ), the equivalent thermal resistance $R_{eq}$ is given by: $\frac{1}{R_{eq}} = \frac{1}{R_1} + \frac{1}{R_2}$ We know that thermal resistance $R = \frac{L}{KA}$ . For the composite rod, the total area is $2A$ , so: $\frac{K_{eq} (2A)}{L} = \frac{K_1 A}{L} + \frac{K_2 A}{L}$ $2K_{eq} = K_1 + K_2$ $K_{eq} = \frac{K_1 + K_2}{2}$

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