BCECE Medical BCECE Medical Solved Papers-2015

  • question_answer
    If a fully charged capacitor C with initial charge \[{{q}_{0}}\] is connected to a coil of self inductance L at\[t=0\]. The time at which the energy is stored equally between the electric field and magnetic field is

    A)   \[\pi \sqrt{LC}\]

    B)  \[\frac{\pi }{4}\sqrt{LC}\]

    C)  \[\frac{\pi }{2}\sqrt{LC}\] 

    D)  \[\frac{\pi }{6}\sqrt{LC}\]

    Correct Answer: B

    Solution :

    In LC oscillation, energy is transferred C to L or L to C, maximum energy in L is \[\frac{1}{2}LI_{\max }^{2}\]. Maximum energy in C is \[\frac{q_{\max }^{2}}{2C}\] Energy will be equal when,                 \[\frac{1}{2}L{{I}^{2}}=\frac{1}{2}\frac{1}{2}LI_{\max }^{2}\Rightarrow I=\frac{{{I}_{\max }}}{\sqrt{2}}\]                 \[I={{I}_{\max }}\sin \omega \,t=\frac{1}{\sqrt{2}}{{I}_{\max }}\]                 \[\omega \,t=\frac{\pi }{4}\Rightarrow \frac{2\pi }{T}\,t=\frac{\pi }{4}\Rightarrow \sqrt{LC}\] \[\Rightarrow \] \[t=\frac{\pi }{4}\sqrt{LC}\]


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