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NEET NEET SOLVED PAPER 2017

  • question_answer
    Two rods A and B of different materials are welded together as shown in figure. Their thermal conductivities are \[{{K}_{1}}\]and \[{{K}_{2}}.\]The thermal conductivity of the composite rod will be                       

    A)  \[2({{K}_{1}}+{{K}_{2}})\]           

    B) \[\frac{{{K}_{1}}+{{K}_{2}}}{2}\]

    C)   \[\frac{3({{K}_{1}}+{{K}_{2}})}{2}\]                       

    D) \[{{K}_{1}}+{{K}_{2}}\]

    Correct Answer: B

    Solution :

                     Thermal current                 \[H={{H}_{1}}+{{H}_{2}}\]                 \[=\frac{{{K}_{1}}A({{T}_{1}}-{{T}_{2}})}{d}+\frac{{{K}_{2}}A({{T}_{1}}-{{T}_{2}})}{d}\]                 \[\frac{{{K}_{EQ}}2A({{T}_{1}}-{{T}_{2}})}{d}=\frac{A({{T}_{1}}-{{T}_{2}})}{d}[{{K}_{1}}+{{K}_{2}}]\]                 \[{{K}_{EQ}}=\left[ \frac{{{K}_{1}}+{{K}_{2}}}{2} \right]\]


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