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Question:

The potential differences of the resistance, the capacitor and the inductor are 80V, 40V and 100V respectively in an LCR circuit. The power factor of the circuit is?

0.5

0.4

1.0

0.8

Solution:

The potential difference across an element in a circuit is given by iX. Hence
80 = iR
40 = iXc
100 = iXl
Power factor of circuit = cosφ = R/Z = R/√((Xl - Xc)² + R²)
= 80/√(100 - 40)² + 80² = 0.8