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An arc lamp operates on a 10 A direct current at 80 V. If the lamp is to be used with a 220 V (rms), 50 Hz alternating supply, the approximate value of the series inductance required is
- 0.044 H
- 0.065 H
- 80 H
- 0.08 H
Correct answer: 0.065 H
Solution
On DC, R = 80/10 = 8 ohm. On AC the lamp still needs 10 A, so Z = 220/10 = 22 ohm. Then wL = sqrt(Z^2 - R^2) = sqrt(484-64) = sqrt(420) ~ 20.5 ohm, and L = 20.5/(2*pi*50) ~ 0.065 H.
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