JEE Main & Advanced Physics Magnetic Effects of Current / करंट का चुंबकीय प्रभाव JEE PYQ-Magnetic Effects Of Current

  • question_answer
    In a certain region static electric and magentic fields exist. The magnetic field is given by \[\vec{B}={{B}_{0}}\left( \hat{i}+2\hat{j}-4\hat{k} \right).\]If a test charge moving with a velocity \[\vec{\upsilon }={{\upsilon }_{0}}\left( 3\hat{i}-\hat{j}+2\hat{k} \right)\]experience no force in that region, then the electric field in the region, in SI units, is - [JEE Online 08-04-2017]

    A) \[\vec{E}=-{{\upsilon }_{0}}{{B}_{0}}\left( \hat{i}+\hat{j}+7\hat{k} \right)\]

    B) \[\vec{E}=-{{\upsilon }_{0}}{{B}_{0}}\left( 3\hat{i}-2\hat{j}-4\hat{k} \right)\]

    C) \[\vec{E}={{\upsilon }_{0}}{{B}_{0}}\left( 14\hat{i}+7\hat{k} \right)\]

    D) \[\vec{E}={{\upsilon }_{0}}{{B}_{0}}\left( 14\hat{j}+7\hat{k} \right)\] 

    Correct Answer: D

    Solution :

    [d] \[{{F}_{e}}={{F}_{n}}=0\]
                \[{{F}_{e}}=-{{F}_{m}}\]
                \[=-q\left( \vec{v}\times \vec{B} \right)\]
                \[=-{{\upsilon }_{0}}{{v}_{0}}\left[ \left( 3\hat{i}-\hat{j}+2\hat{k} \right)\times \left( \hat{i}+2\hat{j}-4\hat{k} \right) \right]\]
                \[=-{{\upsilon }_{0}}{{v}_{0}}\left( 14\hat{i}+7\hat{k} \right)\]


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