Given below are two statements: Statement I: As the frequency of an AC source in a series LCR circuit is increased, the current first increases, reaches a maximum, and then decreases.
Statement II: At resonance in a series LCR circuit, the power factor is one. Choose the correct answer.

Question

Given below are two statements: Statement I: As the frequency of an AC source in a series LCR circuit is increased, the current first increases, reaches a maximum, and then decreases.

Statement II: At resonance in a series LCR circuit, the power factor is one. Choose the correct answer.

G1 Physics · Accepted Answer

In a series LCR circuit, Z = √[R² + (Xₗ - X꜀)²] As frequency increases, X꜀ decreases while Xₗ increases. At resonance, Xₗ=X꜀, so impedance is minimum and current is maximum. Away from resonance, current is smaller. At resonance, phase angle φ = 0, so power factor cosφ = 1. Therefore both statements are true. Hence option D follows.