| English | Electrical power |
|---|---|
| Bahasa Melayu | Kuasa elektrik |
| 中文 | 电功率 |
Definition
The rate at which electrical energy is transferred or used (power = potential difference × current); measured in watts (W).
In exam terms
Electrical power is the rate at which electrical energy is transferred or used. It is measured in watts (W), where 1 W = 1 J s⁻¹, and is calculated from P = VI.
For a resistor this can also be written as P = I²R or P = V²/R. The power rating printed on an appliance tells you how much energy it uses each second at its stated voltage.
Example of correct use: a lamp operating at 240 V and drawing 0.5 A has a power of P = VI = 240 V × 0.5 A = 120 W.
Do not confuse it with…
Do not confuse electrical power with electrical energy. Power is the rate of energy transfer (watts); energy is the total transferred over time (joules), where E = Pt.
A high power rating does not by itself mean a high energy bill, the time the appliance runs matters too.
In Paper 2, you may be asked to calculate the power of an appliance or to compare two appliances; choose the version of the formula (VI, I²R or V²/R) that matches the quantities you are given.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)