Inductive behavior — phase relation: In a predominantly inductive series R–L circuit driven by a sinusoid (|X_L| > R), does the current lag the applied voltage?

Difficulty: Easy

Correct Answer: Yes, current lags the voltage

Explanation:


Introduction / Context:
Knowing whether current leads or lags voltage is central to AC analysis and power factor correction. Inductors store energy in magnetic fields and impose a positive reactive component, shifting current in time relative to voltage.


Given Data / Assumptions:

  • Series R–L circuit, sinusoidal source.
  • |X_L| > R indicates inductive dominance.
  • No capacitor is present in this basic scenario.


Concept / Approach:
In phasor form, Z = R + jX_L. The current phasor I = V/Z lags V by angle φ where tan φ = X_L / R > 0. A positive φ means current lags voltage. As X_L increases or R decreases, φ approaches 90 degrees.


Step-by-Step Solution:

Write Z = R + jX_L.Angle of Z is φ = arctan(X_L / R) > 0.Current angle is −φ relative to voltage → current lags.


Verification / Alternative check:
Oscilloscope with dual channels (voltage and shunt-resistor current sense) shows current zero crossings occurring after voltage zero crossings in inductive circuits.


Why Other Options Are Wrong:

“Leads” describes capacitive behavior (X_C < 0).“In phase” only when X_L ≈ 0 or reactive parts cancel.Capacitor value is irrelevant here; none is present.


Common Pitfalls:
Confusing mnemonic “ELI the ICE man”: voltage (E) leads current (I) in an inductor (L); current leads voltage in a capacitor (C).


Final Answer:
Yes, current lags the voltage

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