PhysicsChapter 6: Alternating Current
Power in AC Circuits
AC power
Definition
AC power is the rate at which alternating electrical energy is transferred or converted.
Pure Resistance
Instantaneous power is: p=vi For a purely resistive circuit, voltage and current are in phase. Using RMS values: Pavg = Vrms Irms For a resistor: Pavg=Irms²R and: Pavg=Vrms²/R For sinusoidal voltage and current with phase difference `φ`: Pavg=Vrms Irms cosφ where: cosφ = power factor For a purely resistive load: **φ=0 therefore: cosφ=1 and: Pavg=VrmsIrms**
Mean and Maximum Power
For an ideal resistive sinusoidal circuit, mean power is half the maximum instantaneous power.
Formula / Key Relation
**P=VrmsIrms cosφ Pure resistor: P=VrmsIrms**
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Power in AC Circuits
Sticky Notes · Quick Revision
AC Power:
- `P=Vrms Irms cosφ`
- Pure R:
- `φ=0`
- `cosφ=1`
60-second revision
- Phase difference determines how much AC power is actually transferred on average.
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