Power
The rate of doing work (energy per unit time).
P = \dfrac{W}{t}
1What it means
Power tells how fast work is done or energy is used. Its SI unit is the watt (W), where 1 W = 1 J/s.
2Variables
| Symbol | Meaning |
|---|---|
| P | Power (watts, W) |
| W | Work done / energy (J) |
| t | Time taken (s) |
3Worked examples
Example 1 Worked solution
Q. A machine does 600 J of work in 4 s. Find its power.
- P = W / t = 600 / 4.
✓ P = 150 W
4Where it's used
- ✦Rating motors, engines and appliances.
- ✦Electricity bills (energy = power × time).
5Tips & common mistakes
- !1 horsepower (hp) ≈ 746 W.
- !For electricity, power is also P = VI.