An alternating voltage of frequency f is applied across a series LCR circuit. Let fr be the resonance frequency for the circuit. Will the current in the circuit lag, lead or remain in phase with the applied voltage when (i) f > fr, (ii) f < fr? Explain your answer in each case.

Solution

Inductive impedence, X_{L} = 2 πfL Capacitive impedence, X_{C} = \frac{1}{2 πfC}

(i) When f > f_r, X_L is large and X_c is small.
The circuit is inductive.
So, current lags behind the applied voltage.

(ii) When f < f_r' X_L is small and X_c is large.
The circuit is capacitive.
So, current leads the voltage in phase.

f_r is the resonant frequency.

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Electrostatic Potential And Capacitance

An alternating voltage of frequency f is applied across a series LCR circuit. Let fr be the resonance frequency for the circuit. Will the current in the circuit lag, lead or remain in phase with the applied voltage when (i) f > fr, (ii) f < fr? Explain your answer in each case.

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