Electricity Units and Safety

IGCSE Edexcel Physics
2.1-2.6 Units and Mains Safety
Key Concepts: Electrical quantities have specific units. Safety devices protect users from electric shock and overheating.

Section A: Units

1. State the SI units for current, charge, voltage, resistance, power, energy and time. [7]

Section B: Safety

2. Explain how insulation and double insulation protect users. [3]
3. Explain how earthing helps protect users. [2]
4. Describe the purpose of a fuse and a circuit breaker. [3]
5. State the difference between AC and DC. [2]
Total marks: 17

Mark Scheme

1. A, C, V, $\Omega$, W, J, s [7]
2. Insulation prevents contact; double insulation uses two layers [3]
3. Provides low-resistance path to earth so current flows safely [2]
4. Fuse melts to break circuit; breaker switches off when current too large [3]
5. AC reverses direction; DC flows one direction [2]