BHU PMT BHU PMT (Screening) Solved Paper-2008

  • question_answer
    A coil has an inductance of 0.7 H and is joined in series with a resistance of\[220\,\Omega \]. When an alternating emf of 220 V at 50 cps is applied to it, then the wattles component of the current in the circuit is

    A)  5 A                                        

    B)  0.5 A

    C)  0.7 A                                    

    D)  7 A

    Correct Answer: B

    Solution :

                     Watt less component of current \[={{I}_{v}}\sin \theta \]                 \[=\frac{{{E}_{v}}}{Z}\sin \theta \]                 \[=\frac{220}{\sqrt{{{R}^{2}}+{{\omega }^{2}}{{L}^{2}}}}\times \frac{\omega L}{\sqrt{{{R}^{2}}+{{\omega }^{2}}{{L}^{2}}}}\]                 \[=\frac{220\times \omega L}{({{R}^{2}}+{{\omega }^{2}}{{L}^{2}})}\]                 \[=\frac{220\times (2\pi \times 50\times 0.7)}{{{(220)}^{2}}+{{(2\pi \times 50\times 0.7)}^{2}}}\]                 \[=\frac{220\times 220}{{{(220)}^{2}}+{{(220)}^{2}}}\]                 \[=\frac{1}{2}\] \[=0.5\text{ }A\]


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