P2 Electricity — Section Overview
Electricity is probably the most practically important section in GCSE Physics. It covers the behaviour of charge in circuits, the quantitative relationships between current, voltage and resistance, and how domestic mains electricity is generated and used safely.
What this section covers
| Sub-topic | Key ideas |
|---|---|
| P2.1 Current, potential difference and resistance | I = Q/t; V = IR; series and parallel circuits |
| P2.2 Series and parallel circuits | Rules for V, I and R in each type |
| P2.3 Domestic electricity | AC vs DC; UK mains (230 V, 50 Hz); plugs, fuses and earthing |
| P2.4 Electrical power | P = IV = I²R = V²/R; E = Pt; kilowatt-hour |
| P2.5 Static electricity | Charging by friction; electric fields; uses and hazards |
Core relationships
Ohm's Law: V = IR — voltage is directly proportional to current at constant temperature for ohmic conductors. Non-ohmic devices (filament bulb, diode) have changing resistance.
Series circuits: current the same throughout; voltages add; total resistance = sum of individual.
Parallel circuits: voltage the same across each branch; currents add; total resistance less than smallest branch.
Power: P = IV. A 60 W bulb running from 230 V draws I = 60/230 ≈ 0.26 A.
Safety in domestic circuits
A fuse or circuit breaker breaks the circuit if current exceeds a safe level. Earth wire provides a low-resistance path to ground if the case becomes live, triggering the fuse. Always choose a fuse just above the normal operating current (not too high — it won't blow fast enough).
Exam focus
- Always check whether a question specifies series or parallel before applying rules.
- Show every step when calculating resistance — examiners award method marks.
- State units explicitly: amperes A, volts (V), ohms (Ω), watts (W), joules (J).
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