A composite flat wall of a furnace is made of two materials 'A' and 'B'. The thermal conductivity of 'A' is twice of that of material 'B', while the thickness of layer of 'A' is half that of B. If the temperature at the two sides of the wall are 400 and 1200°K, then the temperature drop (in °K) across the layer of material 'A' is________________?
Correct answer: D. 160
- A. 125
- B. 133
- C. 150
- D. 160
Explanation
The resistance of layer A is (L_B/2)/(2k_B)=L_B/(4k_B), while that of B is L_B/k_B, so the temperature drops divide in the ratio 1:4. One-fifth of the total 800 K drop occurs across A, giving 160 K.
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