JEE Main & Advanced Sample Paper JEE Main - Mock Test - 41

  • question_answer
    A cylindrical conductor AB of length l and area of cross-section a is connected to a battery having emf E and negligible internal resistance. The specific conductivity of cylindrical conductor varies as \[\sigma ={{\sigma }_{0}}\frac{1}{\sqrt{x}},\]where \[{{\sigma }_{0}}\] is constant and x is distance from end A. What is the electric field just near the end B of cylinder?

    A)             \[\frac{E}{l}\]   

    B)                    \[\frac{2E}{2l}\]

    C)             \[\frac{2E}{3l}\]            

    D)        \[\frac{E}{2l}\]

    Correct Answer: B

    Solution :

    [b] Resistance of cylinder \[R=\int\limits_{0}^{\ell }{\frac{l}{\sigma }\frac{dx}{a}}=\frac{2\sqrt{\ell }}{3a{{\sigma }_{0}}}\] \[I=\frac{E}{R}\] Electric field \[=\frac{J}{\sigma }=\frac{I}{a.\sigma }=\frac{E\sqrt{x}}{Ra{{\sigma }_{0}}\ell }\] At  \[x=\ell \] Electric field  \[=\frac{E\left( \sqrt{\ell } \right)}{\frac{2\sqrt{\ell }}{3a{{\sigma }_{0}}}a{{\sigma }_{0}}\ell }=\frac{3E}{2\ell }\]


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