NEET Sample Paper NEET Sample Test Paper-12

  • question_answer
    A cylindrical rod having temperature\[{{T}_{1}}\]and \[{{T}_{2}}\] at its ends. The rate of flow of heat is \[{{Q}_{1}}\] cal/sec. If all the linear dimensions are doubled keeping temperature constant, then rate of flow of heat \[{{Q}_{2}}\] will be

    A)  \[4\,{{Q}_{1}}\]

    B)  \[2\,{{Q}_{1}}\]

    C)  \[\frac{{{Q}_{1}}}{4}\]

    D)  \[\frac{{{Q}_{1}}}{2}\]

    Correct Answer: B

    Solution :

      Rate of heat flow \[\left( \frac{Q}{t} \right)=\frac{k\pi {{r}^{2}}({{\theta }_{1}}-{{\theta }_{2}})}{L}\propto \frac{{{r}^{2}}}{L}\] \[\therefore \]      \[\frac{{{Q}_{1}}}{{{Q}_{2}}}={{\left( \frac{{{r}_{1}}}{{{r}_{2}}} \right)}^{2}}\left( \frac{{{l}_{2}}}{{{l}_{1}}} \right)={{\left( \frac{1}{2} \right)}^{2}}\times \left( \frac{2}{1} \right)=\frac{1}{2}\] \[\Rightarrow \]\[{{Q}_{2}}=2{{Q}_{1}}\]


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