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SESK: Stuff Everyone Should Know · sesk.info/elec-ac-resistor-phase

In an AC circuit with only a resistor, how do voltage and current line up?

Resistors keep current and voltage in phase.

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  1. Current leads voltage by a quarter cycle
  2. They rise and fall together, in phase ✔
  3. Current lags voltage by a quarter cycle

Why: A resistor does not store energy, so current follows voltage instantly. Capacitors and inductors are what shift the timing.

Huh, didn't know that: OpenStax notes a capacitor stores and releases electric energy, while a resistor turns it into heat.

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References

Answer: They rise and fall together, in phase. A resistor does not store energy, so current follows voltage instantly. Capacitors and inductors are what shift the timing.

  1. OpenStax University Physics Vol. 2, 15.2 Simple AC Circuits openstax.org/books/university-physics-volume-2/pages/15-2-simple-ac-circuits
    the current through and the voltage across the resistor are in phase.
    Checked 2026-10-10.

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