Manipal Medical Manipal Medical Solved Paper-2015

  • question_answer
    In a circuit, L, C and R are connected in series with an alternating voltage source of frequency\[f\].The current leads the voltage by 45°. The value of C is

    A) \[\frac{1}{\pi f(2\pi fL+R)}\]           

    B) \[\frac{1}{\pi f(2\pi fL-R)}\]

    C) \[\frac{1}{2\pi f(2\pi fL-R)}\]         

    D) \[\frac{1}{2\pi f(2\pi fL+R)}\]

    Correct Answer: D

    Solution :

    The phase difference \[\phi \] between current and voltage is given by \[\tan \phi =\frac{{{X}_{L}}-{{X}_{C}}}{R}\]                   \[\frac{{{X}_{L}}-{{X}_{C}}}{R}=\tan {{45}^{\circ }}=1\]                             \[{{X}_{C}}={{X}_{C}}+R\]                      \[\frac{1}{2\pi fC}=2\pi fL+R\]                              \[C=\frac{1}{2\pi (2\pi fL+R)}\]


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