NEET2020Physics-Alternating Current
NEET 2020 Physics LCR Circuits MCQ Question
Type: MCQ-conceptual-Medium-Class 12
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:
A
1.0
B
−1.0
C
zero
D
0.5
Correct Answer
Option A
Detailed Explanation
When L is removed (RC circuit), the phase difference is π/3, meaning tan(π/3) = 1/(ωCR), so XC = R·tan(π/3). When C is removed (RL circuit), the phase difference is again π/3, meaning XL = R·tan(π/3). This means XL = XC, so the full LCR circuit is at resonance and the impedance is purely resistive. Therefore, the power factor cos φ = 1. The correct answer is A.
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