NEET AIPMT SOLVED PAPER 2000

  • question_answer
                    A wire of resistance R is connected in series with an inductor of reactance \[\omega L\].  Then quality factor of RL circuit is:                                                                                                                                                   

    A)                 \[\frac{R}{\omega L}\]                  

    B)                 \[\frac{\omega L}{R}\]                  

    C)                 \[\frac{R}{\sqrt{{{R}^{2}}+{{\omega }^{2}}{{L}^{2}}}}\]  

    D)                 \[\frac{\omega L}{\sqrt{{{R}^{2}}+{{\omega }^{2}}{{L}^{2}}}}\]

    Correct Answer: B

    Solution :

                    We define the quality factor of the circuit as follows:                 Quality factor Q                 \[=2\pi \times \frac{Total\,energy\,stored\,in\,the\,circuit}{Loss\,in\,energy\,in\,each\,cycle}\]                 But the total energy stored in circuit = \[LI_{rms}^{2}\]                 and the energy loss per second = \[I_{rms}^{2}R\]                 So, loss in energy per cycle \[=\frac{I_{rms}^{2}R}{f}\]                 Hence, quality factor \[Q=2\pi \times \frac{LI_{rms}^{2}}{I_{rms}^{2}\,R/f}\]                 \[=\frac{2\pi \,f\,L}{R}=\frac{\omega L}{R}\]                 Note:    Evidently, Q is a dimensionless quantity.


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