In an inductive circuit, the current ______ the voltage?

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Examoogle · Accepted Answer

Lags

Explanation: In a purely inductive circuit, the current lags the applied voltage by exactly $90^\circ$ (or $\frac{\pi}{2}$ radians). This phase shift occurs because the inductor opposes any change in the current flowing through it, resulting in a back-EMF that delays the current peak relative to the voltage peak.

Working Principle: According to Faraday's law, an inductor develops a back-EMF ($e = -L \frac{di}{dt}$) that opposes the change in current. When an alternating voltage $v(t) = V_m \sin(\omega t)$ is applied, the inductor requires time to build up the magnetic flux, causing the current $i(t) = I_m \sin(\omega t - 90^\circ)$ to reach its maximum value later than the voltage.

Key Formulas: $v(t) = V_m \sin(\omega t)$ — Instantaneous voltage; $i(t) = I_m \sin(\omega t - \frac{\pi}{2})$ — Instantaneous current; $X_L = 2\pi fL$ — Inductive reactance

Key Points: Inductors oppose changes in current.; The phase angle $\phi$ is $90^\circ$ for a pure inductor.; The power factor in a purely inductive circuit is zero lagging.; Inductive reactance ($X_L$) increases linearly with frequency ($f$).

Advantages: Used in energy storage devices (magnetic fields).; Essential for filtering and frequency-selective circuits.

Disadvantages: Causes lagging power factor in industrial loads.; Results in increased reactive power (VAR) demand.

Applications: Transformers and motors; Inductor-based low-pass filters; Chokes in fluorescent lamps

Additional Info: A pure inductor does not dissipate power; it only exchanges reactive power.. Option A is incorrect because 'leading' occurs only in capacitive circuits.. Option C and D are incorrect as they compare magnitude, whereas the relationship is phase-based.

Answer: B is correct — In an inductive circuit, the current lags the voltage by a phase angle of $90^\circ$.

Exam Tip: Always remember the mnemonic 'ELI the ICE man': ELI means Voltage (E) Leads Current (I) in an inductor (L), and ICE means Current (I) leads Voltage (E) in a capacitor (C).

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