In alternating-current (AC) analysis of a series RC circuit driven by a sinusoidal source, does the current lag or lead the applied source voltage? Choose the most accurate statement.

Introduction / Context:
The phase relationship between current and voltage is a core concept in AC circuit analysis. In reactive networks, capacitors and inductors shift phase, causing current to lead or lag voltage depending on the component. This question focuses on the classic series RC circuit to test whether you recall which quantity leads and by how much.

Given Data / Assumptions:

• A sinusoidal steady-state source is applied.
• Components are ideal: one resistor R in series with one capacitor C.
• Angular frequency is omega, capacitive reactance is Xc = 1 / (omega * C).
• No measurement loading effects are considered.

Concept / Approach:
The impedance of a series RC circuit is Z = R - jXc. The current I is the same through both elements and equals V / Z. Because the impedance has a negative imaginary part (capacitive), the current phasor leads the voltage phasor by an angle phi where tan(phi) = Xc / R. A helpful memory aid is “ICE” (current leads voltage in a Capacitive circuit; current lags in an Inductive circuit).

Step-by-Step Solution:

Verification / Alternative check:
At very high frequency, Xc approaches 0, so Z approaches R and the phase approaches 0 degrees, consistent with small lead. At very low frequency, Xc is very large, the current is small, and the capacitor dominates, with current attempting to lead by up to 90 degrees in the ideal limit.

Why Other Options Are Wrong:

• “Current lags” is characteristic of inductive circuits, not capacitive ones.
• “Only at low frequencies” is misleading; the lead exists at all frequencies, though the angle varies.
• DC with ripple is irrelevant; pure DC has no steady AC phase, and ripple still follows the AC rule: capacitive currents lead.

Common Pitfalls:
Confusing inductive and capacitive behavior (“ELI the ICE man” mnemonic helps). Another mistake is assuming the phase is fixed; it depends on R and Xc.

Final Answer:
Incorrect — in a series RC circuit, the current leads the source voltage by arctan(Xc/R).