What determines the phase relationship in a purely resistive circuit?

• A. Current leads voltage by 90°
• B. Voltage leads current by 90°
• C. Current and voltage are in phase
• D. Current and voltage are out of phase

Answer: (C)

In a purely resistive circuit, the phase relationship between current and voltage is characterized by both being in phase, which means they reach their peak values and cross zero simultaneously. This is a fundamental property of resistive elements where the impedance is purely resistive, and there is no reactive component contributing to a phase shift.

In such circuits, Ohm's Law (V = IR) applies directly, indicating that any change in voltage results in an instantaneous and proportional change in current without any delay. This behavior is a direct consequence of the absence of inductance or capacitance, which would otherwise introduce phase shifts.

Understanding this concept is crucial for analyzing circuits as it establishes a baseline for comparing how current and voltage behave in other types of circuits that may include reactive components, which shift the phase relationship.