G3 Physics and O-Level Practical Electricity Hub
G3 Physics and O-Level Practical Electricity hub: energy, power, electricity costs, safety devices and home wiring.
Learning goals
- Explain electrical heating in common appliances
- Apply P = VI
- Apply E = VIt
- Calculate electrical energy and cost in kWh
- Identify the hazard from damaged insulation
- Identify the hazard from overheating cables
- Identify the hazard from damp conditions
- Explain how fuses and circuit breakers protect circuits
- Choose and justify an appropriate fuse rating
- Explain why metal casings are earthed
- Explain why double-insulated appliances do not need an earth wire
- State the meanings and roles of live, neutral and earth
- Describe the wiring of a mains plug
- Explain live-wire placement of switches, fuses and circuit breakers
Practical electricity connects circuit physics to appliances, electricity bills and mains safety. Use this hub to move from energy calculations to a complete safety chain: identify the fault, trace the current path, state which device operates and explain why the live supply is isolated.
Before you begin:
- Core Exam Skills (units, graphs, command words)
- D.C. Circuits (Current and P.D. in series/parallel)
- Work, Energy & Power (Definitions of Power and Energy)
Follow this order:
Lessons
1. Energy, power and cost
Heating, Power, Energy & Cost
Heating applications, P = VI, E = VIt, kWh and electricity-cost calculations.
2. Hazards and protection
Electrical Hazards
Shock and fire risks from damaged insulation, overheating cables and damp conditions.
Fuses & Breakers
How protective devices interrupt excessive current and how fuse ratings are selected.
Earthing & Insulation
How earthing metal casings and double insulation reduce electric-shock risk.
3. Mains conductors and wiring
Live, Neutral & Earth
Meanings and normal roles of the three mains conductors.
Live-Wire Switching
Why an open switch must isolate the appliance from the live supply.
Wiring a Mains Plug
Terminal positions, conductor colours, the live fuse and the cable grip.
What you will learn
Each row points to the lesson where the idea is explained and practised.
| You need to be able to… | Learn and practise it here |
|---|---|
| Heating effect in kettles, ovens and heaters | Electric Power & Energy |
| Apply P = VI and E = VIt | Electric Power & Energy |
| Calculate appliance cost using kWh | Electric Power & Energy |
| Hazards from damaged insulation, overheating cables and damp conditions | Dangers Of Electricity |
| Fuses, circuit breakers and fuse ratings | Fuses & Circuit Breakers |
| Earthing metal casings and double insulation | Earthing & Double Insulation |
| Meaning of live, neutral and earth | Electricity In The Home |
| Wiring a mains plug | Wiring A Mains Plug |
| Why switches, fuses and breakers are in the live wire | Switch and Fuses & Circuit Breakers |
Write the sequence explicitly: fault or excess current → protective path/device acts → circuit opens in the live wire → appliance is isolated from the live supply. Do not stop at “the fuse protects the user”.
Revision
Quick Reference
| Quantity / Feature | Detail / Formula | Unit |
|---|---|---|
| Electric Power | P = VI = I² R = V²/R | Watt (W) |
| Electric Energy | E = Pt = VIt | Joule (J) |
| Commercial Energy | E(kWh) = P(kW) × t(h) | kWh |
| Live Wire | Brown (High P.D.) | - |
| Neutral Wire | Blue (0 V return) | - |
| Earth Wire | Green/Yellow (Safety) | - |
1 kWh = 3.6 MJ (1000 W × 3600 s)
Fast workflows (what you do in questions)
- Mains appliance current: I = P/V (use the appliance power rating and the mains voltage).
- Electricity bills: E(kWh) = P(kW) × t(h), then cost = E × tariff.
Wire roles (quick meaning)
- Live: high p.d. relative to Earth (dangerous).
- Neutral: return path, close to 0 V.
- Earth: safety wire; carries current only during a fault.
Quick facts to remember
- Kilowatt-hour (kWh): The amount of energy used by a 1 kW appliance in 1 hour.
- Safety Rule: Switches, fuses, and circuit breakers must always be placed in the Live wire.
- Fuse: A safety device that melts and breaks the circuit if the current exceeds its rating.
- Earthing: Connecting the metal casing of an appliance to the ground to prevent electric shock if a fault occurs.
- Double Insulation: A safety design using two layers of insulation; such appliances do not require an earth wire.
- Damaged Insulation: A hazard where exposed live wires can cause shocks or short circuits.
Fuse choice (exam method)
- Find normal current using I = P/V.
- Choose the next standard fuse rating above the normal current (e.g., 3 A, 5 A, 13 A).
- Explain: too low blows during normal use; too high may not protect the appliance in a fault.
Why earthing works (key idea)
If the live wire touches a metal casing, the earth wire provides a low-resistance path so a large current flows and the fuse/circuit breaker disconnects the supply quickly.
Visual Snapshots (graphs)
These are schematic. Use them to sanity-check energy bills and fuse choices.
Data table
| Usage time | 1 kW heater |
|---|---|
| 1 h | 1 |
| 2 h | 2 |
| 3 h | 3 |
| 4 h | 4 |
| 5 h | 5 |
Data table
| Appliance | Typical operating current |
|---|---|
| Lamp | 0 |
| Iron | 4 |
| Kettle | 9 |
Top Exam Traps
- Fuse Placement: Fuses must be in the live wire. If in the neutral, the appliance stays live even if the fuse blows.
- kWh vs Joules: E = VIt uses seconds (Joules). Electricity bills use kW and hours (kWh). Don’t mix them!
- Earth Current: The earth wire carries current only when there is a fault where the live wire touches the metal casing.
- Choosing Fuse Ratings: Select a fuse slightly higher than the normal operating current (e.g., use a 5A fuse for a 3.5A appliance).
- Dampness: Water is a conductor; using appliances with wet hands significantly reduces body resistance, increasing shock risk.
- Switch placement: Switches must be in the live wire; otherwise the appliance can remain live even when “switched off”.
Practice
Use the Practical Electricity check for power, energy and cost, hazards and protection, and conductors, wiring and isolation, returning to the lesson it identifies whenever an explanation is incomplete.
Then complete the Practical Electricity structured questions for full safety explanations and calculations.
Continue learning
Continue to Magnetism and Electromagnetism, or strengthen investigation skills in the Physics Practical Skills hub.
Course and syllabus information
- Course
- SEC G3 Physics
- Edition
- SEC G3 Physics 2027