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Resistor in AC
Intermediate
Voltage and current are in phase.
Voltage and current are in phase: V = IR at all times and power oscillates at twice the frequency.
Worked example
Heater elements.
Common mistake
No phase shift or reactance.
In more detail
A resistor in an AC circuit has voltage and current in phase, and the current amplitude is V/R. It dissipates power continuously.
Real-world uses
- Heaters and lamps behave like resistors in AC circuits.
- Resistive loads have predictable power consumption on AC supplies.
- A heater resistor in an AC supply has current and voltage rising and falling together, so its power is always positive.
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Frequently asked questions
Does a resistor have phase difference?
No. Voltage and current are in phase for an ideal resistor.
What is its impedance?
Equal to its resistance, R.
Is the resistor's current in phase with voltage?
Yes. For a pure resistor, the current and voltage reach their peaks at the same time.
Related topics in AC Circuits & EM Waves
Peak and RMS values · Average power in AC · Phasors · Inductor in AC · Capacitor in AC · LCR series circuit