JEE Main & Advanced Physics Transmission of Heat Sample Paper Topic Test - Transmission Of Heat

  • question_answer
    A rod of length i and cross section area A has a variable thermal conductivity given by  \[k=\alpha T,\] where a is a positive constant and T is temperature in kelvin. Two ends of the rod are maintained at temperatures \[{{T}_{1}}\] and \[{{T}_{2}}({{T}_{1}}>{{T}_{2}})\]. Heat current flowing through the rod will be

    A) \[\frac{A\alpha (T_{1}^{2}-T_{2}^{2})}{\ell }\]

    B) \[\frac{A\alpha (T_{1}^{2}+T_{2}^{2})}{\ell }\]

    C) \[\frac{A\alpha (T_{1}^{2}+T_{2}^{2})}{3\ell }\]       

    D) \[\frac{A\alpha (T_{1}^{2}-T_{2}^{2})}{2\ell }\]

    Correct Answer: D

    Solution :

    [d] Heat current \[i=-kAdT\]
     \[id=-kA\,dT\]
    \[i\int\limits_{0}^{\ell }{dx}\text{ }=-A\alpha \int\limits_{{{T}_{1}}}^{{{T}_{2}}}{T}\text{ }dT\]
    \[\Rightarrow \]   \[i\,\ell =-A\,\alpha \frac{\left( T_{2}^{2}-T_{1}^{2} \right)}{2}\]
    \[\Rightarrow \]   \[i=\frac{A \alpha \left( T_{1}^{2}-T_{2}^{2} \right)}{2\ell }\]
     


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