In a composite rod, when two rods of different lengths and of the same area are joined end to end, then if $K$ is the effective coefficient of thermal conductivity ; $\frac{{{\ell _1} + {\ell _2}}}{K}$ is equal to
In a composite rod, when two rods of different lengths and of the same area are joined end to end, then if $K$ is the effective coefficient of thermal conductivity ; $\frac{{{\ell _1} + {\ell _2}}}{K}$ is equal to
- A
$\frac{{{\ell _1}}}{{{K_1}}} - \frac{{{\ell _2}}}{{{K_2}}}$
- B
$\frac{{{\ell _1}}}{{{K_2}}} - \frac{{{\ell _2}}}{{{K_1}}}$
- C
$\frac{{{\ell _1}}}{{{K_1}}} + \frac{{{\ell _2}}}{{{K_2}}}$
- D
$\frac{{{\ell _1}}}{{{K_2}}} + \frac{{{\ell _2}}}{{{K_1}}}$
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