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

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

G1 Physics · Accepted Answer

The lamp needs 10 A at 80 V, so R=8 Ω. The required impedance is Z=220/10=22 Ω. Thus Xₗ=√(22²−8²)≈20.49 Ω and L=Xₗ/(2πf)≈0.065 H. Hence option A.