Electrical Power
Understanding electrical power and its calculation in circuits.
What is Electrical Power?
Electrical power is the rate at which electrical energy is transferred by an electric circuit. It is the rate at which work is done or energy is converted from electrical form into another form, such as heat, light, or mechanical energy. The SI unit of electric power is the Watt (W).
Formulas for Electric Power
For DC Circuits:
P = V × I
P = I² × R
P = V² / R
For AC Single-Phase Circuits:
P = V × I × PF
For AC Three-Phase Circuits:
P = √3 × V × I × PF
Where:
• P = Power in Watts (W)
• V = Voltage in Volts (V)
• I = Current in Amperes (A)
• R = Resistance in Ohms (Ω)
• PF = Power Factor (for AC circuits)
P = V × I
P = I² × R
P = V² / R
For AC Single-Phase Circuits:
P = V × I × PF
For AC Three-Phase Circuits:
P = √3 × V × I × PF
Where:
• P = Power in Watts (W)
• V = Voltage in Volts (V)
• I = Current in Amperes (A)
• R = Resistance in Ohms (Ω)
• PF = Power Factor (for AC circuits)
Units of Electric Power
| Unit | Symbol | Description |
|---|---|---|
| Watt | W | The SI unit of power, equal to one Joule per second. |
| Kilowatt | kW | 1,000 Watts, commonly used for household appliance power ratings. |
| Megawatt | MW | 1,000,000 Watts, used for large power generation. |
| Horsepower | hp | A non-SI unit of power, often used for motors (1 hp ≈ 746 W). |
Frequently Asked Questions
What is the difference between electric power and electric energy?
Electric power is the rate at which energy is consumed or produced (e.g., Watts). Electric energy is the total amount of power consumed or produced over a period of time (e.g., Watt-hours or Joules).
Why is power factor important in AC power calculations?
In AC circuits, power factor accounts for the phase difference between voltage and current. It determines how much of the apparent power is actually converted into useful work (real power).