JEE Main & Advanced Sample Paper JEE Main Sample Paper-20

  • question_answer
    A dipole consisting of two charges \[+q\] and \[-q\] joined by a  massless rod of length \[\ell ,\] is seen oscillating with a small  amplitude in a uniform electric field of magnitude E. The period of oscillation                                         

    A)  is proportional to E                              

    B)  is proportional to 1/E     

    C)  is \[\pi \sqrt{\frac{m\ell }{3qE}}\]                             

    D)  is proportional to \[\frac{1}{\sqrt{E}}\] but \[\ne \pi \sqrt{\frac{m\ell }{3qE}}\]

    Correct Answer: C

    Solution :

     \[I=\frac{m{{\ell }^{2}}}{12};\] Restoring troque \[=qE\ell \sin \theta \approx qE\ell \theta =\frac{{{d}^{2}}\theta }{d{{t}^{2}}}\]             \[\therefore \] \[\omega =\sqrt{\frac{qE\ell }{I}}=\sqrt{\frac{qE\ell \times 12}{m{{\ell }^{2}}}}=\frac{2\pi }{T}\]                 \[\therefore \] \[T=\pi \sqrt{\frac{m\ell }{3qE}}\]


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