NEET Sample Paper NEET Sample Test Paper-89

  • question_answer
    If electronic charge e, electron mass m, speed of light in vacuum c and Planck's constant h are taken as fundamental quantities, the permeability of vacuum \[{{\mu }_{0}}\] can be expressed in units of

    A) \[\left( \frac{h}{m{{e}^{2}}} \right)\]

    B)                    \[\left( \frac{hc}{m{{e}^{2}}} \right)\]

    C) \[\left( \frac{h}{c{{e}^{2}}} \right)\]     

    D)        \[\left( \frac{m{{c}^{2}}}{h{{e}^{2}}} \right)\]

    Correct Answer: C

    Solution :

    [c] Let \[{{\mu }_{0}}\] related with e, m, c and h as follows. \[{{\mu }_{0}}=k{{e}^{a}}{{m}^{b}}{{c}^{c}}{{h}^{d}}\] \[[ML{{T}^{-2}}{{A}^{-2}}]={{[AT]}^{a}}{{[M]}^{^{b}}}{{[L{{T}^{-1}}]}^{c}}{{[M{{L}^{2}}{{T}^{-1}}]}^{d}}\] \[=[{{M}^{b+d}}\,\,{{L}^{c+2d}}\,\,{{T}^{a-c-d}}\,\,{{A}^{a}}]\] On comparing both sides we get \[a=-2\]                                     ...(i) \[b+d=1\]                                 ...(ii) \[c+2d=1\]                                ...(iii) \[a-c-d=-2\]                                ...(iv) By equation (i), (ii), (iii) & (iv) we get, \[a=-2,\]\[b=0,\]\[c=-1,\]\[d=1\] \[\therefore \]\[[{{\mu }_{0}}]=\left[ \frac{h}{c{{e}^{2}}} \right]\]


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