JEE Main & Advanced Sample Paper JEE Main Sample Paper-8

  • 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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