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

In a purely resistive load, the current and voltage are indeed in phase, meaning they oscillate together without any phase difference. When a sinusoidal voltage is applied to a resistive circuit, the current that flows through the resistor reaches its maximum and minimum values at the same points in time as the voltage does. This is characterized by a phase angle of 0 degrees as there is no lag or lead between the two waveforms.

This concept stems from Ohm's Law, which states that the current through a resistor is directly proportional to the voltage across it and inversely proportional to the resistance of the circuit. Since there are no reactive components, such as inductors or capacitors, present to introduce any phase shift, the current and voltage maintain a constant relationship throughout the cycle, confirming that they are in phase.