NEET Physics Mathematical Tools, Units & Dimensions NEET PYQ-Mathematical Tools, Units and Dimensions

  • question_answer
    A physical quantity of the dimensions of length that can be formed out of c, G and \[\frac{{{e}^{2}}}{4\pi {{\varepsilon }_{0}}}\] is [c is velocity of light, G is universal constant of gravitation and e is charge]          [NEET-2017]

    A)                        \[\frac{1}{c}G\frac{{{e}^{2}}}{4\pi {{\varepsilon }_{0}}}\]

    B) \[\frac{1}{{{c}^{2}}}{{\left[ G\frac{{{e}^{2}}}{4\pi {{\varepsilon }_{0}}} \right]}^{\frac{1}{2}}}\]

    C) \[{{c}^{2}}{{\left[ G\frac{{{e}^{2}}}{4\pi {{\varepsilon }_{0}}} \right]}^{\frac{1}{2}}}\]

    D) \[\frac{1}{{{c}^{2}}}{{\left[ \frac{{{e}^{2}}}{G4\pi {{\varepsilon }_{0}}} \right]}^{\frac{1}{2}}}\]

    Correct Answer: B

    Solution :

    [b] Let \[\frac{{{e}^{2}}}{4\pi {{\varepsilon }_{0}}}=A=M{{L}^{3}}{{T}^{-2}}\]
    \[l={{C}^{x}}{{G}^{y}}{{(A)}^{z}}\]
    \[L={{[L/{{T}^{-1}}]}^{x}}{{[{{M}^{-1}}{{L}^{3}}{{T}^{-2}}]}^{y}}{{[M{{L}^{3}}{{T}^{-2}}]}^{z}}\]
    \[-y+z=0\Rightarrow y=z\]                           …(i)
    \[x+3y+3z=1\]                                   …(ii)
    \[-x-4z=0\]                                          …(iii)
    From (i), (ii) & (iii)
    \[z=y=\frac{1}{2},\,x=-2\]


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