IGCSE Physics Electrical Safety Questions and Worked Solutions (4.4) | 0625

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IGCSE Physics 0625 · Topic 4.4

IGCSE Physics Electrical Safety Questions and Worked Solutions

50 topic-wise practice questions on Electrical Safety (Unit 4: Electricity and Magnetism), written to the Cambridge IGCSE Physics 0625 syllabus for 2026–2028, each with a step-by-step worked solution.

50 questions40 Core0 Extended10 Challenge125 marksTextbook §4.4 · pp. 222–228
Questions tagged Core are for all candidates (Papers 1 & 3). Questions tagged Extended are Supplement content (Papers 2 & 4). Questions 41–50 are harder Challenge questions. Try each question first, then tap Show solution to check your working.

Topic guide: Electrical Safety

Mains electricity can be dangerous. Safety features — insulation, fuses, trip switches, earthing and double insulation — protect people and wiring.

Key formulas

I = P ÷ Vchoose a fuse just above the normal currentCore

Prerequisite knowledge

  • Power P = IV (4.2.5)
  • Current and circuits (4.2, 4.3)

Exam tips & common mistakes

  • Common fuse ratings: 3 A, 5 A, 13 A — choose the smallest above the normal current
  • Explain the earth wire as a sequence: fault → large current → fuse melts → live disconnected
  • 'Live wire' and 'line wire' mean the same

Key facts from the syllabus (4.4)

  • Hazards: damaged insulation, overheating cables, damp conditions, overloaded plugs/extension leads/sockets
  • Mains circuits have live, neutral and earth wires
  • Switches and fuses go in the live wire so the appliance is disconnected from the high p.d. when off
  • A fuse melts and breaks the circuit if the current is too high; a trip switch (circuit breaker) opens automatically and can be reset
  • Metal-cased appliances are earthed: a fault causes a large current to earth that blows the fuse
  • Double-insulated appliances have non-conducting casings and need no earth; the fuse still protects the cable

Textbook: §4.4 Electrical safety, pp. 222–228

1
Core[2 marks]

State the hazard of damaged insulation on a cable.

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Method: Live wire exposed.

The live wire may be exposed, causing electric shock or fire
2
Core[2 marks]

State the hazard of overheating cables.

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Method: Fire.

Insulation can melt, leading to fire or exposed wires
3
Core[2 marks]

State why using electrical appliances in damp conditions is dangerous.

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Method: Water conducts.

Water can conduct current through a person, causing electric shock
4
Core[2 marks]

State the hazard of overloading a multiple socket.

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Method: Excess current.

Too much current flows, overheating the cables and possibly causing fire
5
Core[1 mark]

Name the three wires in a mains circuit.

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Method: Live, neutral, earth.

Live (line), neutral and earth
6
Core[2 marks]

Explain why a switch must be connected in the live wire.

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Method: Isolates the appliance.

So that when it is switched off, the appliance is disconnected from the high p.d. and is safe
7
Core[2 marks]

Explain how a fuse protects a circuit.

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Method: Melts when current too high.

If the current exceeds the rating, the thin wire melts and breaks the circuit, preventing overheating
8
Core[2 marks]

Explain how a trip switch (circuit breaker) works and one advantage over a fuse.

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Method: Electromagnet trips switch.

It detects a large current and switches off automatically; it can be reset rather than replaced and acts faster
9
Core[3 marks]

A 230 V kettle has power 2.3 kW. Available fuses are 3 A, 5 A, 13 A. Choose the correct fuse.

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Method: I = P/V = 10 A.

I = 2300 ÷ 230 = 10.0 A; use the 13 A fuse
10
Core[3 marks]

A 230 V lamp has power 60 W. Available fuses are 3 A, 5 A, 13 A. Choose the correct fuse.

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Method: I = 0.26 A.

I = 60 ÷ 230 = 0.261 A; use the 3 A fuse
11
Core[2 marks]

Explain why a fuse rating should be just above the normal operating current.

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Method: Not too high, not too low.

So it does not blow in normal use but melts quickly if a fault causes a larger current
12
Core[3 marks]

Explain how the earth wire protects a user of an appliance with a metal casing.

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Method: Low resistance path, large current blows fuse.

If the live wire touches the casing, a large current flows through the low-resistance earth wire, blowing the fuse and disconnecting the supply
13
Core[2 marks]

Explain why the outer casing of an appliance must be either earthed or non-conducting.

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Method: Prevents casing becoming live.

To prevent the casing becoming live and giving a shock if a fault occurs
14
Core[2 marks]

Explain why a double-insulated appliance does not need an earth wire.

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Method: Plastic casing cannot become live.

Its outer casing is non-conducting, so it cannot become live
15
Core[1 mark]

State what a fuse protects in a double-insulated appliance without an earth wire.

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Method: Circuit and cabling.

The circuit and the cabling
16
Core[3 marks]

A 1.2 kW toaster runs on 230 V. Calculate the normal current and choose between 3 A, 5 A, 13 A fuses.

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Method: I = 5.2 A.

I = 1200 ÷ 230 = 5.22 A; use the 13 A fuse
17
Core[2 marks]

Explain why the fuse is placed in the live wire.

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Method: Disconnects from high p.d.

So that when it melts, the appliance is disconnected from the live supply
18
Core[3 marks]

A 230 V hairdryer has power 900 W. Calculate the current and choose a suitable fuse from 3 A, 5 A, 13 A.

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Method: I = 3.9 A.

I = 900 ÷ 230 = 3.91 A; use the 5 A fuse
19
Core[2 marks]

Explain why electrical sockets are not placed near baths or showers.

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Method: Damp conditions.

Water conducts electricity, increasing the risk of a fatal electric shock
20
Core[2 marks]

State what colour-coding helps with in a mains plug.

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Method: Identify wires.

It makes it easy to identify live, neutral and earth wires so they are connected correctly
21
Core[2 marks]

State the colour of the live, neutral and earth wires in modern UK/European plugs.

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Method: Brown, blue, green-yellow.

Live: brown; neutral: blue; earth: green and yellow
22
Core[2 marks]

State the approximate p.d. of the live wire relative to earth in mains supply (e.g. 230 V countries).

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Method: 230 V.

About 230 V
23
Core[2 marks]

State the p.d. of the neutral wire relative to earth.

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Method: ~0 V.

About 0 V
24
Core[2 marks]

Explain why touching the live wire is dangerous even with the switch on the appliance off, if the switch is in the neutral wire.

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Method: Still live.

The appliance is still connected to the live wire, so parts remain at a high p.d.
25
Core[3 marks]

A 230 V iron has power 1.0 kW. Choose a fuse from 3 A, 5 A and 13 A.

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Method: I = 4.3 A.

I = 4.35 A; 5 A fuse
26
Core[3 marks]

A 230 V computer uses 400 W. Choose a fuse from 3 A, 5 A and 13 A.

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Method: I = 1.7 A.

I = 1.74 A; 3 A fuse
27
Core[3 marks]

A 230 V heater uses 2.8 kW. Choose a fuse from 3 A, 5 A and 13 A.

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Method: I = 12.2 A.

I = 12.2 A; 13 A fuse
28
Core[2 marks]

Explain why a 13 A fuse should not be used in a lamp cable that normally carries 0.3 A.

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Method: Too high rating.

A fault current could overheat the thin cable before the fuse melts
29
Core[2 marks]

State two advantages of a circuit breaker over a fuse.

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Method: Resettable, fast.

It can be reset; it acts faster
30
Core[2 marks]

Explain why cables with damaged insulation should be replaced.

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Method: Shock and fire.

Exposed wires can cause electric shock or short circuits and fires
31
Core[2 marks]

Explain why plugging too many appliances into one socket is dangerous.

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Method: Overload.

The total current may be too large, overheating the socket and cable and causing a fire
32
Core[2 marks]

State the purpose of the earth wire.

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Method: Safety path.

To provide a low-resistance path to earth if the metal casing becomes live
33
Core[2 marks]

Explain why a thicker cable is used for a cooker than for a lamp.

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Method: Larger current.

A cooker draws a larger current; a thick cable has lower resistance so it does not overheat
34
Core[3 marks]

Describe what happens, step by step, when the live wire in an earthed kettle touches its metal casing.

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Method: Fault sequence.

Current flows from live through the casing and earth wire; the low resistance gives a very large current; the fuse melts, disconnecting the live wire so the casing is safe
35
Core[2 marks]

Explain why double-insulated appliances have the symbol of a square within a square.

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Method: Identification.

It shows the appliance is double-insulated and does not need an earth wire
36
Core[2 marks]

Explain why bathroom light switches are often pull-cords.

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Method: Damp hands.

They keep wet hands away from electrical contacts
37
Core[2 marks]

State why the fuse rating chosen should be slightly above the normal current.

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Method: Not blow in normal use.

So it does not melt during normal operation but does melt with a fault
38
Core[2 marks]

Explain how a residual current device (trip switch) protects people.

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Method: Detects imbalance.

It detects a difference between live and neutral currents (current leaking to earth) and switches off quickly
39
Core[3 marks]

A 230 V hair straightener draws 0.35 A. Calculate its power and choose a fuse (3 A, 5 A, 13 A).

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Method: P = IV.

P = 80.5 W; 3 A fuse
40
Core[2 marks]

Explain why using electrical appliances outdoors in the rain is dangerous.

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Method: Damp.

Water can conduct current from live parts through the user

Challenge questions

Harder, multi-step questions at the top end of the exam. Attempt these once you are confident with the questions above.

41
ChallengeCore[4 marks]

A 230 V heater rated 2.5 kW is connected with a 5 A fuse by mistake. Explain what will happen and choose the correct fuse from 3 A, 5 A, 13 A.

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Method: I = 10.9 A.

I = 10.9 A — the 5 A fuse will melt as soon as it is switched on; use the 13 A fuse
42
ChallengeCore[4 marks]

Explain in detail how the earth wire and the fuse work together to protect a person if the live wire touches the metal case of a washing machine.

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Method: Fault sequence.

Current flows from live through the case and the low-resistance earth wire to earth; the current is very large, the fuse melts and disconnects the live supply, so the case is not left live
43
ChallengeCore[4 marks]

Explain why the switch and fuse must be in the live wire and not the neutral, describing what would happen otherwise.

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Method: Appliance stays live.

If in the neutral, opening the switch or blowing the fuse would leave the appliance connected to the live wire at 230 V, so touching it could cause a shock
44
ChallengeCore[3 marks]

Explain why a double-insulated hairdryer does not need an earth wire but still needs a fuse.

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Method: Casing non-conducting.

The plastic casing cannot become live; the fuse still protects the cable from overheating if there is a fault
45
ChallengeCore[4 marks]

An extension lead is rated 13 A. A 2.0 kW heater, a 1.2 kW kettle and a 0.80 kW iron are plugged in at 230 V. Determine whether it is overloaded and explain the danger.

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Method: Total current.

I = 4000 ÷ 230 = 17.4 A > 13 A: overloaded — the cable may overheat and cause a fire
46
ChallengeCore[4 marks]

Compare a fuse and a trip switch (circuit breaker), giving two advantages of a trip switch.

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Method: Reset and speed.

Both cut the current when it is too high; a trip switch can be reset rather than replaced and acts faster (some also detect leakage to earth)
47
ChallengeCore[3 marks]

Explain why damaged insulation is dangerous even if the appliance still works.

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Method: Exposed live.

Bare live wires can be touched, causing a shock, or touch other conductors causing short circuits and fires
48
ChallengeCore[4 marks]

A 230 V freezer draws 0.70 A normally but 3.5 A briefly when starting. Choose a fuse from 3 A, 5 A, 13 A and explain.

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Method: Start-up surge.

5 A: a 3 A fuse could blow at each start; 13 A would give poor protection
49
ChallengeCore[3 marks]

Explain why water and electricity are a dangerous combination in bathrooms, and give two safety measures.

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Method: Water conducts.

Water lowers the resistance of the skin and can conduct current; measures: pull-cord switches, no sockets near baths, RCD protection
50
ChallengeCore[4 marks]

A cable with resistance 0.20 Ω carries 25 A in an overloaded circuit. Calculate the power wasted in the cable and explain the risk.

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Method: P = I²R (or I × V).

P = 25² × 0.20 = 125 W — the cable heats up and its insulation may melt, causing a fire
All IGCSE Physics topics← 4.3.3 Action and Use of Circuit Components4.5.1 Electromagnetic Induction →

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