CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2007

  • question_answer
    An inductance of \[\left( \frac{200}{\pi } \right)\,mH\], a capacitance of \[\left( \frac{{{10}^{-3}}}{\pi } \right)F\]and a resistance of \[10\,\Omega \] are connected in series with an AC source 220 V, 50 Hz. The phase angle of the circuit is

    A)  \[\frac{\pi }{6}\]                                             

    B)  \[\frac{\pi }{4}\]

    C)                  \[\frac{\pi }{2}\]                                             

    D)                  \[\frac{\pi }{3}\]

    Correct Answer: B

    Solution :

    The phase angle \[(\theta )\] between \[I\] and V is given by                 \[\tan \theta =\frac{{{X}_{L}}-{{X}_{C}}}{R}\]                      ... (i) where, \[{{X}_{L}}=2\pi fL\]                 \[=2\pi \times 50\times \left[ \frac{200}{\pi }\times {{10}^{-3}} \right]\]                 \[=20\,\Omega \]                 \[{{X}_{C}}=\frac{1}{2\,\pi fC}\]                 \[=\frac{1\times \pi }{2\pi \times 50\times {{10}^{-3}}}\]                 \[=10\,\,\Omega \] and        \[R=10\text{ }\Omega \] Substituting values of \[{{X}_{L}},\,{{X}_{C}}\] and R in Eq. (i), we get                 \[\tan \theta =\frac{20-10}{10}=1\] \[\Rightarrow \]               \[\tan \theta =\tan \frac{\pi }{4}\] \[\therefore \]  \[\theta =\frac{\pi }{4}\] The phase angle of the circuit is \[\frac{\pi }{4}\].


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