MGIMS WARDHA MGIMS WARDHA Solved Paper-2014

  • question_answer
    An AC source, of voltage\[V={{V}_{m}}\sin \omega t,\]is applied across a series RC circuit in which the capacitive impedance is a times the resistance in the circuit. The value of the power factor of the circuit is

    A)  \[0\]                                    

    B)  \[1/\sqrt{1+{{a}^{2}}}\]

    C)  \[\sqrt{1+{{a}^{2}}}\]                   

    D)  None of these

    Correct Answer: B

    Solution :

                    Since, capacitive impedance is a times the resistance in the RC series AC circuit. Therefore,                 \[{{Z}^{2}}={{R}^{2}}+X_{C}^{2}\] According to the question                 \[{{X}_{C}}=aR\] Therefore,                 \[{{Z}^{2}}={{R}^{2}}+{{a}^{2}}{{R}^{2}}\]                 \[Z=R\sqrt{1+{{a}^{2}}}\] Power factor \[\cos \phi =R/Z=1/\sqrt{1+{{a}^{2}}}\]


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