Power is the rate of doing work or transferring energy. This guide covers definition, types, units, conversion, measurement, and applications.
What is Power?
P = W/t. SI unit: watt (W) = joule/second. Higher power → faster work transfer.
Key Concept:
Energy is capacity; power is how fast energy is used/transferred.
Types of Power
Mechanical
Force×velocity or torque×angular speed. Example: engine power.
Electrical
P = V×I. Example: appliances.
Thermal
Rate of heat transfer (W, BTU/h). Heating systems.
Optical
Radiant flux; optics applications.
Units of Power
SI Units
- W
- kW
- MW
- GW
Other Units
- hp: 745.7 W
- BTU/h: 0.2931 W
- ft·lb/s: 1.356 W
- cal/s: 4.1868 W
Power Conversion Table
| Unit | Watts (W) | Horsepower (hp) | BTU/h |
|---|---|---|---|
| 1 W | 1 | 0.001341 | 3.412 |
| 1 hp | 745.7 | 1 | 2,545 |
| 1 BTU/h | 0.2931 | 0.000393 | 1 |
Measuring Power
Wattmeter
Voltage×current in electrical systems.
Dynamometer
Torque and rpm → power (engines/motors).
Calorimeter
Heat flow → thermal power.
Applications of Power
Energy production
- Plant output
- Renewables
- Generator sizing
- Storage
Transportation
- Engines
- Aircraft
- Marine
- EVs
Electronics
- PSUs
- Amplifiers
- Computing
- Batteries
Industrial
- Manufacturing
- Robotics
- Pumps/Compressors
- HVAC
Did You Know?
Three Gorges Dam ≈ 22,500 MW capacity; enough for 10M+ homes.
Power in Everyday Life
Household appliances
- LED 5–15 W
- Laptop 50–100 W
- Fridge 100–400 W
- Microwave 600–1,200 W
- Dryer 1,800–5,000 W
- AC 3,500–5,000 W
Human power
- Rest ~100 W
- Manual work ~75 W
- Cycling 100–200/400+ W
- Sprinter ~2,600 W
Practical Tip:
Check both power (W) and energy (Wh). Short, high‑power use can consume less energy than long, low‑power use.