Power Energy
AC Power
In an AC circuit the product of RMS voltage and RMS current gives apparent power in volt-amperes. The active power that actually does work is that product multiplied by the power factor, cos φ, which accounts for the phase difference between voltage and current. A load with a poor power factor draws more current for the same active power, which increases losses and equipment loading.
AC Power
P = V_rms × I_rms × cos φ
Variables and units
| Symbol | Quantity | Unit |
|---|---|---|
| P | Active power | W |
| V_rms | RMS voltage | V |
| I_rms | RMS current | A |
| cos φ | Power factor | dimensionless |
Conditions of application
Sinusoidal steady state with RMS values. Apparent power is S = V_rms × I_rms; active power is S × cos φ. For non-sinusoidal waveforms, use the appropriate power definitions rather than a single phase angle.
Worked example
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Real, reactive and apparent power from RMS voltage, current and power factor.