JEE Main & Advanced Sample Paper JEE Main Sample Paper-33

  • question_answer
    In a region of space magnetic field exists in a cylindrical region of radius 'a' centered at origin. The field is given by: \[\overrightarrow{B}={{B}_{0}}t\hat{k}\]. There for experienced by a stationary charge q placed at (r,0,0) where r > a, is:

    A)  \[q{{B}_{0}}\].            

    B)    \[\frac{{{q}_{0}}{{B}_{0}}{{a}^{2}}}{2r}\]

    C)  \[\frac{q,{{B}_{0}}r}{2}\]        

    D)    zero

    Correct Answer: B

    Solution :

    \[\oint{\vec{E}.d\vec{l}\,=\frac{-d\phi }{dt}=\frac{-dBA}{dt}={{B}_{0}}\pi {{a}^{2}}}\]             \[\Rightarrow \,\,E2\pi r\,={{B}_{0}}\pi {{a}^{2}}\,\Rightarrow \,E=\frac{{{B}_{0}}{{a}^{2}}}{2r}\]             \[F=qE=\frac{q\,{{B}_{0}}\,{{a}^{2}}}{2r}\]


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