If the sine waves of voltage and current pass through zero at the same instant and peak at the same instant, they are in what condition?

• A. In phase
• B. Out of phase
• C. Phase shift
• D. Amplitude mismatch

Answer: (A)

Phase alignment between voltage and current is what’s being shown here. If the two sinusoidal waves cross zero at the same time and reach their peaks at the same moment, they share the same phase angle, meaning there is zero phase difference. This in-phase relationship means the current follows the voltage without leading or lagging, which corresponds to a unity power factor typical of a purely resistive circuit.

If there were a lead or lag between them, you’d have a phase shift and they wouldn’t peak or cross zero together. Amplitude differences alone don’t determine the timing; you can have different peak values yet still be in phase if their timing matches.