Electrical Power and Energy Transfer in Appliances — AQA GCSE Physics
Electrical power is the rate at which an appliance transfers energy. It links current, potential difference and resistance.
Electrical power
Power is the rate of energy transfer (in watts). For electrical circuits:
$$P = V \times I \qquad P = I^2 \times R$$
- P = power (W), V = potential difference (V), I = current (A), R = resistance (Ω).
Use P = VI when you know p.d. and current; use P = I²R when you know current and resistance.
Energy transferred
The energy transferred by an appliance depends on its power and the time it operates: $$E = P \times t$$ You can also use E = Q × V (energy = charge × potential difference).
Worked example
A 230 V kettle draws a current of 10 A.
- Power = V × I = 230 × 10 = 2300 W (2.3 kW).
- In 2 minutes (120 s): E = 2300 × 120 = 276 000 J.
Power ratings
The power rating of an appliance (e.g. 2000 W) tells you how much energy it transfers each second. Higher-power appliances transfer more energy in a given time.
Exam tips
- Learn P = VI and P = I²R and when to use each.
- Energy transferred: E = Pt (or E = QV).
- Watch units (time in seconds; convert kW to W).
- Power rating = energy transferred per second.