NEET Physics Thermometry, Calorimetry & Thermal Expansion NEET PYQ-Thermometry, Calorimetry and Thermal Expansion

  • question_answer
    A copper rod of 88 cm and an aluminium rod of unknown length have their increase in length independent of increase in temperature. The length of aluminium rod is-                                                                       [NEET 2019]
    \[({{\alpha }_{Cu}}=1.7\times {{10}^{5}}\text{ }{{K}^{1}}\text{ }and\,{{\alpha }_{Al}}=\]\[~2.2\times {{10}^{5}}\text{ }{{K}^{1}})\]

    A)  88 cm

    B)       68 cm

    C)  6.8 cm

    D)       113.9 cm

    Correct Answer: B

    Solution :

    [b] \[\Delta {{\ell }_{1}}=\Delta {{\ell }_{2}}\]
    \[{{\ell }_{1}}{{\alpha }_{1}}={{\ell }_{2}}{{\alpha }_{2}}\]
    \[\frac{{{\ell }_{1}}}{{{\ell }_{2}}}=\frac{{{\alpha }_{2}}}{{{\alpha }_{1}}}\]
    \[\frac{88}{{{\ell }_{a}}}=\frac{2.2\times {{10}^{-5}}}{1.7\times {{10}^{-5}}}\]
    \[{{\ell }_{a}}=68cm\]
    Comment: In this question it should be difference in length instead of increase in length.

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