JEE Main & Advanced JEE Main Paper (Held On 11 April 2015)

  • 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: JEE Main Online Paper (Held On 11 April 2015)

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

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

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

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

    Correct Answer: C

    Solution :

      \[\left[ e \right]=IT\] \[\left[ m \right]=M\] \[\left[ c \right]=L{{T}^{-1}}\] \[\left[ h \right]=M{{L}^{2}}{{T}^{-1}}\] \[\left[ {{\mu }_{0}} \right]=ML{{I}^{-2}}{{T}^{-3}}\] If \[{{\mu }_{0}}={{e}^{a}}{{m}^{b}}{{c}^{c}}{{h}^{d}}\] \[ML{{T}^{-2}}{{T}^{-3}}={{\left[ IT \right]}^{a}}{{\left[ M \right]}^{b}}{{\left[ L{{T}^{-1}} \right]}^{c}}{{\left[ M{{L}^{2}}{{T}^{-1}} \right]}^{d}}\] by equating powers, we get \[a=-2,b=0,c=-1,d=1\] \[\therefore \] \[\left[ {{\mu }_{0}} \right]=\left[ \frac{h}{c{{e}^{2}}} \right]\]


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