VIT Engineering VIT Engineering Solved Paper-2015

  • question_answer
    The masses of three copper wires are in the ratio 2:3:5 and their lengths are in the ratio 5:3:2.Then, the ratio of their electrical resistances is

    A) 1:9:15                   

    B) 2:3:5

    C) 5:3:2                     

    D) 125:30:8

    Correct Answer: D

    Solution :

    As we know that                        \[{{T}_{1/2}}=4.47\times {{10}^{8}}yr\] So       \[{{R}_{1}}:{{R}_{2}}:{{R}_{3}}=\frac{{{l}_{1}}}{{{A}_{1}}}:\frac{{{l}_{2}}}{{{A}_{2}}}:\frac{{{l}_{3}}}{{{A}_{3}}}\]              \[=\frac{l_{1}^{2}}{{{V}_{1}}}:\frac{l_{2}^{2}}{{{V}_{2}}}:\frac{l_{3}^{2}}{{{V}_{3}}}\] \[=\frac{l_{1}^{2}}{({{m}_{1}}d)}:\frac{l_{2}^{2}}{({{m}_{2}}d)}:\frac{l_{3}^{2}}{({{m}_{3}}d)}\] \[=\frac{l_{1}^{2}}{{{m}_{1}}}:\frac{l_{2}^{2}}{{{m}_{2}}}:\frac{l_{3}^{2}}{{{m}_{3}}}\]              \[n\times 0.3=1-0.778=0.22\]              \[n=\frac{0.222}{0.3}=0.74\]


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