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JEE Main & Advanced Sample Paper JEE Main - Mock Test - 18

  • question_answer
    An electric dipole of length 1 cm is placed with the axis making an angle of \[30{}^\circ \]with an electric field of strength \[{{10}^{4}}\text{N}\,{{\text{C}}^{-1}}\]. If it experiences a torque of \[10\sqrt{2}\,\text{N}\,\text{m,}\]the potential energy of the dipole is

    A) 0.245 J          

    B) 2.45 J

    C) 0.0245 J         

    D) 24.5 J

    Correct Answer: D

    Solution :

    [d]: Here, \[\tau =pE\sin \theta \] \[10\sqrt{2}=p\times {{10}^{4}}\sin {{30}^{o}}={{10}^{4}}\times \frac{P}{2}\] \[p=\frac{20\sqrt{2}}{{{10}^{4}}}=2\sqrt{2}\times {{10}^{-3}}\] \[P.E.=pE\cos \theta \] \[=2\sqrt{2}\times {{10}^{-3}}\times {{10}^{4}}\cos {{30}^{o}}=20\sqrt{2}\times \frac{\sqrt{3}}{2}\] \[=10\sqrt{6}\times 10\times 2.45J=24.5J\]


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