For a purely resistive load, what is the phase relationship between voltage and current?

For a purely resistive load, what is the phase relationship between voltage and current?

• A. They are out of phase by 180 degrees.
• B. Current leads voltage by 90 degrees.
• C. They are in phase (0° phase difference).
• D. Current and voltage are opposite in phase by 180 degrees.

Answer: (C)

For a purely resistive load, voltage and current are in phase. This comes straight from Ohm’s law: V = I × R. With resistance fixed, the current follows the voltage waveform exactly, so they reach their peaks and zero crossings at the same instants. There’s no energy stored in the circuit to cause a delay or advance, as happens with inductors (current lags voltage) or capacitors (current leads voltage). Therefore the phase difference is 0 degrees, meaning voltage and current are in sync.

For a purely resistive load, voltage and current are in phase. This comes straight from Ohm’s law: V = I × R. With resistance fixed, the current follows the voltage waveform exactly, so they reach their peaks and zero crossings at the same instants. There’s no energy stored in the circuit to cause a delay or advance, as happens with inductors (current lags voltage) or capacitors (current leads voltage). Therefore the phase difference is 0 degrees, meaning voltage and current are in sync.