JEE Main & Advanced Sample Paper JEE Main - Mock Test - 43

  • question_answer
    A parallel plate air capacitor has a capacitance C. When it is half filled with a dielectric of dielectric constant 5, the percentage increase in the capacitance will be

    A) \[400%\]

    B)        \[66.6%\]

    C) \[33.3%\]

    D)        \[200%\]

    Correct Answer: D

    Solution :

    \[C=\frac{{{\varepsilon }_{0}}A}{d}\] and \[C'=\frac{{{\varepsilon }_{0}}A}{2d}+\frac{{{\varepsilon }_{0}}\left( 5A \right)}{2d}\] \[=\frac{{{\varepsilon }_{0}}A}{2d}(1+5)=\frac{6{{\varepsilon }_{0}}A}{2d}=\frac{3{{\varepsilon }_{0}}A}{d}\] \[\Rightarrow \,\,\Delta C=C'-C=\frac{3{{\varepsilon }_{0}}A}{d}-\frac{{{\varepsilon }_{0}}A}{d}=\frac{2{{\varepsilon }_{0}}A}{d}\] Percentage change in capacitance \[\frac{\Delta C}{C}=\frac{\frac{2{{\varepsilon }_{0}}A}{d}}{\frac{{{\varepsilon }_{0}}A}{d}}\times 100%=200%\]


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