MGIMS WARDHA MGIMS WARDHA Solved Paper-2010

  • question_answer
    An L-C-R series circuit consists of a resistance of 10 \[\Omega \] a capacitor of reactance 6.0 \[\Omega \]and an inductor coil. The circuit is found to resonate when put across a 300 V, 100 Hz supply- The inductance of coil is (take \[\pi \] = 3)

    A)  0.1 H                                    

    B)  0.01 H

    C)  0.2 H                                    

    D)  0.02 H

    Correct Answer: A

    Solution :

                     Angular velocity, \[{{\omega }_{0}}=2\pi \,n=2\pi \times 100\] \[{{\omega }_{0}}=2\times 3\times 100=600\,rad/s\]\[(\because \pi =3)\] Further                   \[{{\omega }_{0}}=\frac{1}{\sqrt{LC}}\]                                ... (i) Also       \[{{X}_{C}}=\frac{1}{C{{\omega }_{0}}}=60\,\Omega \] \[\Rightarrow \]               \[C=\frac{1}{{{\omega }_{0}}\times 60}=\frac{1}{600\times 60}\] \[\Rightarrow \]               \[C=\frac{1}{36\times {{10}^{3}}}F\] So, put values in Eq. (i), we get \[600=\frac{1}{\sqrt{L\left( \frac{1}{36\times {{10}^{3}}} \right)}}\] \[36\times {{10}^{4}}=\frac{36\times {{10}^{3}}}{L}\] \[\Rightarrow \]               \[L=\frac{36\times {{10}^{3}}}{36\times {{10}^{4}}}=\frac{1}{10}=0.1H\]


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