Power Energy
Electrical Power
Electrical power is the rate at which electrical energy is transferred. For a resistive load it can be calculated as P = V × I, and by substituting Ohm’s law it can also be written as P = I² × R or P = V² ÷ R. The three forms are equivalent for a resistance; choose the one that matches the quantities you know. Power is measured in watts, where 1 W = 1 J/s.
Electrical Power
P = V × I = I² × R = V² ÷ R
Variables and units
| Symbol | Quantity | Unit |
|---|---|---|
| P | Power | W |
| V | Voltage | V |
| I | Current | A |
| R | Resistance | Ω |
Conditions of application
For a resistive DC load, or the instantaneous power of an AC load. For AC power over time, use RMS values together with the power factor.
Worked example
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Calculate DC power from voltage, current or resistance using P = VI, P = I²R and P = V²/R.