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A series circuit contains a resistor R, an inductor L, a capacitor C, and an a.c. source. If the inductor is taken out, the phase angle between the applied voltage and the current becomes π/3. If the capacitor is instead removed, the phase angle is again π/3. What is the power factor of the original circuit?
- 1/2
- 1/√2
- 1
- √3/2
Correct answer: 1
Solution
Removing L gives an RC circuit with tan(phi)=Xc/R; removing C gives an RL circuit with tan(phi)=XL/R. Both angles equal pi/3 means XL=XC, so the circuit is at resonance, net reactance is zero, and the power factor cos(phi)=1.
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