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CMC Medical CMC-Medical Ludhiana Solved Paper-2015

  • question_answer
    The dimension of a room is\[4m\times 4m\times 10\,cm\] end of concrete roof \[(K=1.26\,W{{m}^{-1}}{}^\circ {{C}^{-1}}).\] At some instant, the temperature outside is \[46{}^\circ \]and that inside of room is\[32{}^\circ C\]. Neglecting the convection, amount of heat flouring per second into the room through the roof, will be

    A)  2890 W               

    B)  2830 W

    C)  2800 W               

    D)  2822 W

    Correct Answer: D

    Solution :

                    The area of roof \[A=4\times 4=16\,{{m}^{2}}\] Thickness, \[x=10\text{ }cm=0.10\text{ }m\] The thermal resistance of the roof is \[R=\frac{x}{KA}=\frac{1}{1.26}\times \frac{0.10}{16}\]    \[=4.96\times {{10}^{-3}}\,{}^\circ C{{W}^{-1}}\] \[\therefore \]Rate of heat flow (i.e. heat current) \[\frac{\Delta Q}{\Delta t}=\frac{{{T}_{1}}-{{T}_{2}}}{R}=\frac{46{}^\circ C-32{}^\circ C}{4.96\times {{10}^{-3}}\,{}^\circ C{{W}^{-1}}}\] \[\Rightarrow \]               \[\frac{\Delta Q}{\Delta t}=2822\,W\]


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