In an AC circuit, the power factor changes from 1/2 to 1/4 while the resistance remains unchanged. By what percentage should the impedance be increased to achieve this change in power factor?

100%
200%
50%
25%

Correct answer: 100%

Solution

With R constant, Z1 = R/(1/2) = 2R and Z2 = R/(1/4) = 4R. The percentage increase in impedance is (4R - 2R)/(2R) * 100 = 100%.

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