JEE Main & Advanced Sample Paper JEE Main - Mock Test - 29

  • question_answer
    A thin copper wire of length L increases its length by 1% when heated from temperature \[{{T}_{1}}\]to \[{{T}_{2}}\]. What is the percentage change in area when a thin copper plate having dimensions \[2L\times L\] is heated from\[{{T}_{1}}\] to\[{{T}_{2}}\]?

    A) 0.5%    

    B) 1%  

    C) 2%       

    D) 4%

    Correct Answer: C

    Solution :

    [c] : Length of the wire at temperature\[{{T}_{2}}\] is \[{{L}_{t}}=L\left( 1+\frac{1}{100} \right)\therefore 2L_{t}^{2}=2{{L}^{2}}{{\left( 1+\frac{1}{100} \right)}^{2}}\] Now \[2L_{t}^{2}=\]area of the plate at temperature \[{{T}_{2}}({{A}_{t}})\]and \[2L_{{}}^{2}=\]area of the plate at temperature\[{{T}_{1}}(A)\]. \[\therefore \]\[{{A}_{t}}=A{{\left( 1+\frac{1}{100} \right)}^{2}}=A\left( 1+\frac{2}{100} \right)=\frac{102A}{100}\] Thus, the area increases by 2%.


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