In AC circuit fundamentals, which description best characterizes a purely capacitive circuit under sinusoidal excitation?

Introduction / Context:
Understanding limiting cases such as purely capacitive or purely inductive circuits builds intuition for impedance, phase, and power behavior in AC systems. This question probes recognition of what opposes current and the associated phase relationships in an ideal capacitor-only circuit.

Given Data / Assumptions:

• Sinusoidal steady-state operation.
• No resistive component present (ideal capacitor only).
• Standard sign convention for phase: current leads voltage in a capacitor.

Concept / Approach:
In a pure capacitive circuit, the impedance is Xc = 1 / (2 * pi * f * C) and is entirely reactive. There is no real (resistive) part, so the only opposition to current is capacitive reactance. The current leads the voltage by 90 degrees, which implies voltage lags by 90 degrees, not leads.

Step-by-Step Solution:

Verification / Alternative check:
Using phasors, Z = −jXc has zero real part; hence only reactive opposition exists and phase shift is −90 degrees for voltage relative to current.

Why Other Options Are Wrong:

Common Pitfalls:
Mixing up phase lead/lag signs; assuming some resistance is always present in idealized examples.

Final Answer:
Capacitive reactance provides the only opposition to current flow.