In pure inductor circuit, which quantity is leading

Question

Examoogle · Accepted Answer

Option B: Voltage

Explanation & Concepts:
In a purely inductive circuit, the voltage across the inductor leads the current flowing through it by an angle of $90^\circ$ (or $\frac{\pi}{2}$ radians). This phase shift occurs because the induced electromotive force (EMF) opposes the change in current.

Working Principle: When an alternating current flows through an inductor, it creates a changing magnetic flux, which induces a self-back EMF according to Faraday's Law ($e = -L \frac{di}{dt}$). To overcome this back EMF, the source voltage must lead the current such that the current is zero when the rate of change of current is maximum, resulting in the $90^\circ$ phase lag of current relative to voltage.

Key Formulas: $v(t) = V_m \sin(\omega t)$ — Instantaneous voltage; $i(t) = I_m \sin(\omega t - 90^\circ)$ — Instantaneous current; $X_L = 2\pi fL$ — Inductive reactance

Key Points: The power factor in a pure inductor is $\cos(90^\circ) = 0$.; Average power consumed by a pure inductor over a full cycle is zero.; Inductors oppose the change in current, leading to the phase difference.

Advantages: No active power consumption (ideal case).; Essential for filtering and energy storage in magnetic fields.

Disadvantages: Practical inductors have internal resistance (DC resistance).; Cannot change current instantaneously.

Applications: Transformers and Motors; Inductive filters and Tuning circuits

Additional Info: In a purely capacitive circuit, the current leads the voltage by $90^\circ$.. Option A is incorrect because current lags behind the voltage in an inductive circuit.

Answer: B is correct — In a pure inductive circuit, the voltage leads the current by exactly $90^\circ$ due to the back EMF generated by the inductor.

Exam Tip: Remember the mnemonic 'ELI the ICE man': In an Inductor (L), E (Voltage) leads I (Current); in a Capacitor (C), I (Current) leads E (Voltage).

Examoogle · Answer

Option A: Current

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