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Standard XIII

Physics

Conduction Law

A composite w...

Question

A composite wall having three layers of thickness $0.3 m$ , $0.2 m$ and $0.1 m$ and of thermal conductivity $0.6, 0.4$ and $0.1 W/m-K$ respectively, has a surface area of $1 m^{2} .$ If the inner and outer temperatures of the composite wall are $1840 K$ and $340 K$ respectively, find the rate of heat transfer.

150 W

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150 W

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75 W

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750 W

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Solution

The correct option is D $750 W$
We know that, rate of flow of heat $H = \frac{T_{i} - T_{o}}{R_{e q}}$ .
Since the area of the slabs remain same , the slabs are connected in series combination.
So, $R_{e q} = \sum \frac{L}{K A}$
$\Rightarrow H = \frac{1840 - 340}{\frac{0.3}{0.6 \times 1} + \frac{0.2}{0.4 \times 1} + \frac{0.1}{0.1 \times 1}} \Rightarrow H = 750 W$
Thus, option (d) is the correct answer.

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