Physics 0625 · syllabus 4.4
Cambridge IGCSE Physics 0625 — Electrical safety topical past papers
The hazards of mains electricity, live, neutral and earth wires, how fuses and trip switches work and are chosen, and how earthing and double insulation protect users.
- Questions
- 1,322
- Years
- 2009–2026
- With mark scheme
- 99%
- Questions 2022–2026
- 484
Anyone can browse these pages. Opening the questions and their mark schemes takes a free Momentum account.
What Electrical safety covers
Mains electricity can kill, and the hazards are specific. Damaged insulation can leave a live wire exposed to touch; a cable carrying more current than it was made for overheats and can start a fire; water in damp conditions conducts, so current can pass through a person; and plugging too many appliances into one socket or extension lead draws more current than it can safely carry.
A mains circuit has three wires. The live (or line) wire is at a high voltage, the neutral wire completes the circuit, and the earth wire is a safety connection that normally carries no current. Switches and fuses are placed in the live wire, so that when a switch is off or a fuse has blown the appliance is cut off from the high voltage; a switch in the neutral wire would turn the appliance off but leave it live.
A fuse contains a thin wire that melts when the current exceeds its rating, breaking the circuit; a trip switch, or circuit breaker, cuts the current in the same situation and can be reset. The rating chosen should be a little above the normal working current. An appliance with a metal case has the case connected to the earth wire: if a fault makes the case live, a large current flows to earth, which blows the fuse or trips the switch, instead of passing through someone who touches it. A double-insulated appliance has a non-conducting outer casing instead and needs no earth wire, but it still has a fuse to protect the circuit and its cable. This is all Core content, tested on every written paper.
In the syllabus
The headings this topic has in the Cambridge International 2026–2028 syllabus, as the board prints them.
- 4.4 Electrical safety
What you should be able to do
- State the hazards of damaged insulation, overheating cables, damp conditions and overloaded sockets
- Identify the live, neutral and earth wires, and explain why switches and fuses go in the live wire
- Explain how a fuse and a trip switch protect a circuit
- Choose a suitable fuse or trip switch rating from an appliance's power and voltage
- Explain how an earthed metal case and double insulation each protect the user
Key ideas
- Live: high voltage; neutral: completes the circuit; earth: a safety path that normally carries no current
- Switches and fuses are connected in the live wire
- Fuse rating: the next value above the normal working current, which is found from I = P/V
- Earthed metal case: a fault current flows to earth and blows the fuse or trips the switch
- Double-insulated appliances have a non-conducting casing and no earth wire; the fuse protects the circuit and cable
How Electrical safety has been examined
From 2022 to 2026, Electrical safety was on Paper 4 · Theory (Extended) in 14 of 14 exam series, worth about 17% of that paper’s marks.
| Paper | Questions | Share of marks | Series |
|---|---|---|---|
| Paper 1 · Multiple Choice (Core) | 183 | 14% | 14 of 14 |
| Paper 2 · Multiple Choice (Extended) | 170 | 13% | 14 of 14 |
| Paper 3 · Theory (Core) | 47 | 14% | 14 of 14 |
| Paper 4 · Theory (Extended) | 52 | 17% | 14 of 14 |
| Paper 6 · Alternative to Practical | 32 | 25% | 13 of 14 |
Momentum’s own count, over the questions in its bank for these years: a series is one exam session, every zone included, and a question filed under two chapters counts in both. Median marks per question: 1. The bank files this topic together with neighbouring ones, so these figures count every question in its chapters, including some on those topics.
Filed in Momentum under: Electricity.
A worked example
A 2.3 kW heater and a 60 W lamp each run from a 230 V supply, and the fuses on sale are rated 3 A, 5 A and 13 A. Find the working current of each appliance and choose a fuse for each.
- Heater: I = P/V = 2300 / 230 = 10 A, so it needs the 13 A fuse
- Lamp: I = P/V = 60 / 230 = 0.26 A, so the 3 A fuse is the right choice
- With a 13 A fuse, a fault could drive a current far too large for the lamp's thin cable before the fuse melted, so the cable could overheat
Answer: Heater 10 A, with a 13 A fuse; lamp 0.26 A, with a 3 A fuse
Written by Momentum for this page, with its own numbers; it is not taken from a past paper.
Mistakes that cost marks
- Choosing a fuse rated below the working current, or far above it — too low and it blows in normal use; too high and the cable can overheat before it melts
- Saying the earth wire protects the appliance — it protects the user, by giving a fault current an easy path so that the fuse blows
- Saying a fuse stops you getting a shock — it melts when the current is too large for the cable; it is the earth connection, together with the fuse, that makes a faulty metal case safe
- Putting the switch in the neutral wire — the appliance would stay connected to the live wire even when switched off
- Saying a double-insulated appliance needs no fuse — it needs no earth wire, but its fuse still protects the circuit and the cable
Exam technique
- For fuse questions, calculate I = P/V, then choose the smallest rating above that current from the list given
- When explaining earthing, give the sequence: fault, case becomes live, large current to earth, fuse melts or switch trips, supply cut off
- Name the hazard precisely — electric shock, overheating or fire — rather than writing that something is 'dangerous'
Practising in Momentum
- Every question in a chapter as one list, from every paper and year in the bank, newest first or shuffled.
- Each question turns over to its own part of the mark scheme, where the board published one.
- Narrow by paper, year, session, zone and marks, and star the questions worth keeping.
- Pick chapters, a number of questions and a time, and the exam builder draws a mock to sit and mark.
Past-paper questions and mark schemes are the copyright of Cambridge International. Momentum shows them to signed-in learners for revision and does not publish them on these pages.