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NEET Sample Paper NEET Sample Test Paper-69

  • question_answer
    The coefficients of thermal conductivity of copper, mercury and glass are respectively \[{{K}_{m}}\,\,and\,\,{{K}_{g}}\] such that\[{{K}_{c}}>{{K}_{m}}>{{K}_{g}}\]. If the same quantity of heat is to flow per second per unit area of each and corresponding temperature gradients are \[{{X}_{c}},\,\,{{X}_{m}}\,\,and\,\,{{X}_{g}}\], then

    A) \[{{X}_{c}}={{X}_{m}}={{X}_{g}}\]

    B) \[{{X}_{c}}>{{X}_{m}}>{{X}_{g}}\]c

    C) \[{{X}_{c}}<{{X}_{m}}<{{X}_{g}}\]

    D) \[{{X}_{m}}<{{X}_{c}}<{{X}_{g}}\]  

    Correct Answer: C

    Solution :

    \[\frac{Q}{At}=K\frac{\Delta \theta }{l}\,\,\,\,\,\,\,\,\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,K\frac{\Delta \theta }{l}=cons\tan t\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\frac{\Delta \theta }{l}\propto \frac{1}{K}\] Hence If \[{{K}_{c}}>{{K}_{m}}>{{K}_{g}}\], then \[{{\left( \frac{\Delta \theta }{l} \right)}_{c}}<{{\left( \frac{\Delta \theta }{l} \right)}_{m}}<{{\left( \frac{\Delta \theta }{l} \right)}_{g}}\] \[\Rightarrow \,\,\,\,{{X}_{c}}<{{X}_{m}}<{{X}_{g}}\] because higher K implies lower value of the temperature gradient.


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