JEE Main & Advanced Physics Alternating Current / प्रत्यावर्ती धारा Question Bank Critical Thinking

  • question_answer
    A telephone wire of length 200 km has a capacitance of 0.014 mF per km. If it carries an ac of frequency 5 kHz, what should be the value of an inductor required to be connected in series so that the impedance of the circuit is minimum

    A)            0.35 mH                                  

    B)            35 mH

    C)            3.5 mH                                    

    D)            Zero

    Correct Answer: A

    Solution :

                       Capacitance of wire                    \[C=0.014\times {{10}^{-6}}\times 200=2.8\times {{10}^{-6}}F=2.8\mu F\] For impedance of the circuit to be minimum \[{{X}_{L}}={{X}_{C}}\] Þ \[2\pi \nu L=\frac{1}{2\pi \nu C}\] Þ\[L=\frac{1}{4{{\pi }^{2}}{{\nu }^{2}}C}=\frac{1}{4{{(3.14)}^{2}}\times {{(5\times {{10}^{3}})}^{2}}\times 2.8\times {{10}^{-6}}}\] \[=0.35\times {{10}^{-3}}H=0.35\,mH\]


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