Q14 / 44 · NTA Abhyas (JEE Main) 2020 · Physics · Alternating Current

A telephone wire of length 200 km has a capacitance of 0.014 μF km-1. If it carries an AC frequency of  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?

  • Correct answer
    A
    0.35 mH
  • B
    3.5 mH
  • C
    2.5 mH
  • D
    zero

Solution

Capacitance of wire

C=0.014×10-6×200

=2.8×10-6 F=2.8 μF

For impedance of the circuit to be minimum

XL=XC

⇒2πfL=12πfC

L=14π2f2C

=143.142×5×1032×2.8×10-6

=0.35×10-3 H=0.35 mH

Hence, the correct answer is option: 'A'.

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