JEE Main & Advanced JEE Main Paper (Held On 11 April 2015)

  • question_answer
    A beaker contains a fluid of density\[\rho \,kg/{{m}^{3}},\] specific heat \[S\text{ }J/kg{}^\circ C\]and viscosity t| . The beaker is filled up to height h. To estimate the rate of heat transfer per unit area \[(\overset{\bullet }{\mathop{Q}}\,/A)\]by convection when beaker is put on a hot plate, a student proposes that it should depend on \[\eta ,\left( \frac{S\Delta \theta }{h} \right)\]and\[\left( \frac{1}{\rho g} \right)\]when \[\Delta \theta \] (in \[{}^\circ C\] ) is the difference in the temperature between the bottom and top of the fluid. In that situation the correct option for \[(\overset{\bullet }{\mathop{Q}}\,/A)\]is: [JEE Main Online Paper (Held On 11 April 2015)]  

    A) \[\eta \frac{S\Delta \theta }{h}\]

    B) \[\eta \left( \frac{S\Delta \theta }{h} \right)\left( \frac{1}{\rho g} \right)\]

    C) \[\frac{S\Delta \theta }{\eta h}\]

    D) \[\left( \frac{S\Delta \theta }{\eta h} \right)\left( \frac{1}{\rho g} \right)\]

    Correct Answer: A

    Solution :

    Let \[\left( \frac{\theta }{A} \right)\]is derived quantity which is derived by three fundamental quantities \[\eta ,\left( \frac{S\Delta \theta }{h} \right)\]and\[\left( \frac{1}{eg} \right)\]By using property of homogeneity. \[\left[ \frac{\theta }{A} \right]={{\left[ \eta  \right]}^{x}}{{\left[ \frac{S\Delta \theta }{h} \right]}^{y}}{{\left[ \frac{1}{eg} \right]}^{z}}\] \[\left[ \frac{\theta }{A} \right]=\left[ {{m}^{1}}{{T}^{-3}} \right]\]   \[\left[ \eta  \right]=\left[ {{m}^{1}}{{L}^{-1}}{{T}^{-1}} \right]\] \[\left[ \frac{S\Delta \theta }{h} \right]=\left[ {{L}^{-1}}{{T}^{-2}} \right]\] \[\left[ \frac{1}{eg} \right]=\left[ {{m}^{-1}}{{L}^{2}}{{T}^{+2}} \right]\] \[\left[ {{m}^{1}}{{L}^{0}}{{T}^{-3}} \right]={{\left[ {{m}^{1}}{{L}^{-1}}{{T}^{-1}} \right]}^{x}}{{\left[ {{m}^{0}}{{L}^{1}}{{T}^{-2}} \right]}^{y}}{{\left[ {{m}^{1}}{{L}^{2}}{{T}^{+2}} \right]}^{z}}\]\[x+0-z=1,-x+y+2z=0\And -x-2y+2z=-3\]\[-x+y+2z=0\]     \[-x-2y+2z=-3\] \[\frac{+\,\,+-\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,+\,\,\,\,\,\,\,\,\,\,\,\,\,}{3y=3\Rightarrow y=1,}x=1,z=0\] So, \[\frac{\theta }{A}=\eta .\frac{S\Delta \theta }{h}\]


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