JEE Main & Advanced Physics Thermometry, Calorimetry & Thermal Expansion Question Bank Critical Thinking

  • question_answer
    The coefficient of linear expansion of crystal in one direction is \[{{\alpha }_{1}}\] and that in every direction perpendicular to it is \[{{\alpha }_{2}}\]. The coefficient of cubical expansion is

    A)            \[{{\alpha }_{1}}+{{\alpha }_{2}}\]                                  

    B)            \[2{{\alpha }_{1}}+{{\alpha }_{2}}\]

    C)            \[{{\alpha }_{1}}+2{{\alpha }_{2}}\]                               

    D)            None of these

    Correct Answer: C

    Solution :

                       \[V={{V}_{0}}(1+\gamma \Delta \theta )\] \[{{L}^{3}}={{L}_{0}}(1+{{\alpha }_{1}}\Delta \theta )L_{0}^{2}{{(1+{{\alpha }_{2}}\Delta \theta )}^{2}}\]\[=L_{0}^{3}(1+{{\alpha }_{1}}\Delta \theta )\,{{(1+{{\alpha }_{2}}\Delta \theta )}^{2}}\] Since \[L_{0}^{3}={{V}_{0}}\] and \[{{L}^{3}}=V\] Hence \[1+\gamma \Delta \theta =(1+{{\alpha }_{1}}\Delta \theta )\,{{(1+{{\alpha }_{2}}\Delta \theta )}^{2}}\] \[\tilde{=}\,(1+{{\alpha }_{1}}\Delta \theta )\,(1+2{{\alpha }_{2}}\Delta \theta )\] \[\tilde{=}\,(1+{{\alpha }_{1}}\Delta \theta +2{{\alpha }_{2}}\Delta \theta )\] Þ g = a1 + 2a2


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