NEET 2020 · PhysicsPower factorPrevious Year Question
A series LCR circuit is connected to an ac voltage source. When L is removed from the circuit, the phase difference between current and voltage is π/3. If instead C is removed from the circuit, the phase difference is again π/3 between current and voltage. The power factor of the circuit is
Answer: (A) 1.0. Answer: (A) 1.0 Solution: When L is removed (only R and C): tan(π/3) = X_C/R, so X_C = R√3.
- A.1.0✓
- B.-1.0
- C.Zero
- D.0.5
Correct Answer
(A) 1.0
Solution & Explanation
Answer: (A) 1.0 Solution: When L is removed (only R and C): tan(π/3) = X_C/R, so X_C = R√3. When C is removed (only R and L): tan(π/3) = X_L/R, so X_L = R√3. Therefore X_L = X_C, meaning the full LCR circuit is at resonance. At resonance the net reactance is zero, impedance Z = R, the phase difference is 0, and power factor cos φ = R/Z = 1.0.
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