If the load on a circuit is purely resistive, what can be said about the phase angle between voltage and current?

• A. They are 90 degrees
• B. They are 0 degrees
• C. They are 180 degrees
• D. They are 45 degrees

Answer: (B)

When the load is purely resistive, voltage and current are in phase. This happens because a resistor follows Ohm’s law V = IR, with no reactive component to store or release energy. As a result, the current waveform rises and falls exactly with the voltage waveform, giving a phase angle of zero degrees. The power factor is 1, meaning all the power is real power with no reactive component. If the load were inductive, the current would lag behind the voltage by 90 degrees; if capacitive, the current would lead by 90 degrees; a 45-degree difference wouldn’t occur for a purely resistive load.