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JEE Main 2016 · Power, Power Factor & Wattless Current

Power, Power Factor & Wattless Current question from JEE Main 2016

Q68JEE Main 2016Medium

Power, Power Factor & Wattless Current

An arc lamp requires a direct current of 10 A at 80 V to function. If it is connected to a 220 V (rms), 50 Hz AC supply, the series inductor needed for it to work is close to:

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Answer: (b)

$R = 80/10 = 8\ \Omega$ , $Z = 220/10 = 22\ \Omega$ .
$X_L = \sqrt{22^2 - 8^2} = \sqrt{420} \approx 20.5\ \Omega$
$L = \frac{20.5}{2\pi\times 50} \approx 0.065$ H, so the answer is (b).

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