Six wires each of cross-sectional area $A$ and length $l$ are combined as shown in the figure. The thermal conductivities of copper and iron are $K_1$ and $K_2$ respectively. The equivalent thermal resistance between points $A$ and $C$ is
Six wires each of cross-sectional area $A$ and length $l$ are combined as shown in the figure. The thermal conductivities of copper and iron are $K_1$ and $K_2$ respectively. The equivalent thermal resistance between points $A$ and $C$ is
- A
$\frac{{l({K_1} + {K_2})}}{{{K_1}{K_2}A}}$
- B
$\frac{{2l({K_1} + {K_2})}}{{{K_1}{K_2}A}}$
- C
$\frac{l}{{({K_1} + {K_2})A}}$
- D
$\frac{{2l}}{{({K_1} + {K_2})A}}$
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