IGCSE Physics Electric Current Questions and Worked Solutions (4.2.2) | 0625

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IGCSE Physics 0625 · Topic 4.2.2

IGCSE Physics Electric Current Questions and Worked Solutions

50 topic-wise practice questions on Electric Current (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 questions19 Core21 Extended10 Challenge119 marksTextbook §4.2 · pp. 184–208
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: Electric Current

Electric current is a flow of charge. In metals, the charge carriers are free electrons. Current is measured with an ammeter connected in series.

Key formulas

I = Q ÷ tcurrent I (A), charge Q (C), time t (s)Extended
1 A = 1 C/sdefinition of the ampereExtended

Prerequisite knowledge

  • Charge (4.2.1)
  • Converting minutes/hours to seconds

Exam tips & common mistakes

  • Convert mA to A (÷ 1000)
  • Convert minutes to seconds before using Q = It
  • Current is not 'used up' in a circuit

Key facts from the syllabus (4.2.2)

  • Current is related to the flow of charge
  • Ammeters (analogue and digital) are connected in series; choose a suitable range
  • Conduction in metals is due to the movement of free electrons
  • d.c. flows in one direction (cells); a.c. changes direction repeatedly (mains)
  • Extended current is the charge passing a point per unit time
  • Extended conventional current flows from + to −; electrons flow from − to +

Textbook: §4.2 Electrical quantities, pp. 184–208

1
Core[1 mark]

State what an electric current is.

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Method: Flow of charge.

A flow of charge
2
Core[1 mark]

State the instrument used to measure current and how it is connected.

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Method: Ammeter in series.

An ammeter, connected in series
3
Core[2 marks]

Describe electrical conduction in a metal.

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Method: Free electrons.

Free electrons move through the metal lattice, carrying charge
4
Core[2 marks]

State the difference between direct current and alternating current.

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Method: One direction vs reversing.

d.c. flows in one direction only; a.c. repeatedly changes direction
5
Core[1 mark]

Give one source of d.c. and one source of a.c.

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Method: Cell vs mains.

d.c.: a cell/battery; a.c.: the mains supply
6
Core[2 marks]

An ammeter has ranges 0–1 A and 0–10 A. A current is about 0.4 A. State which range to use and why.

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Method: Most precise suitable range.

0–1 A: it gives a more precise reading and the current is within range
7
Core[1 mark]

State the unit of current.

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Method: Ampere.

ampere (A)
8
Core[2 marks]

Explain why an ammeter should have a very low resistance.

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Method: Doesn't reduce current.

So it does not significantly reduce the current it is measuring
9
Core[2 marks]

Describe the difference between reading an analogue and a digital ammeter.

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Method: Scale vs display.

Analogue: read the pointer position on a scale (avoid parallax); digital: read the number directly
10
Core[1 mark]

State what happens to the current in a circuit if the circuit is broken.

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Method: No current.

The current stops (falls to zero)
11
Core[2 marks]

Explain why current is the same everywhere in a simple loop circuit.

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Method: Charge not used up.

Charge is not used up; the same charge flows through every part per second
12
Core[2 marks]

Describe the reading on an analogue ammeter where the needle is between 0.3 A and 0.4 A, nearer 0.4 A.

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Method: Estimate.

About 0.37 A (read to the nearest half division)
13
Core[2 marks]

State why an ammeter is connected in series.

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Method: Measure current through component.

So that all the current through the component also passes through the ammeter
14
Core[2 marks]

Give two differences between a.c. and d.c.

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Method: Direction, source.

a.c. reverses direction repeatedly and comes from the mains/generators; d.c. flows in one direction and comes from cells
15
Core[2 marks]

State the frequency of the mains a.c. supply in many countries.

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Method: 50 Hz.

50 Hz (60 Hz in some countries)
16
Core[2 marks]

Describe what happens to the free electrons in a wire when a cell is connected.

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Method: Drift.

They drift through the wire from the negative terminal towards the positive terminal
17
Core[2 marks]

Convert 350 mA into amperes.

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Method: ÷ 1000.

0.35 A
18
Core[2 marks]

Convert 0.025 A into milliamperes.

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Method: × 1000.

25 mA
19
Core[2 marks]

Describe how to measure a current of about 2 mA with a digital multimeter.

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Method: Range and connection.

Select the mA (e.g. 20 mA) current range and connect the meter in series
20
Extended[1 mark]

Define electric current.

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Method: I = Q/t.

The charge passing a point per unit time
21
Extended[2 marks]

A charge of 30 C passes a point in 15 s. Calculate the current.

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Method: I = Q ÷ t.

I = 30 ÷ 15 = 2.00 A
22
Extended[2 marks]

A current of 0.25 A flows for 2.0 minutes. Calculate the charge.

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Method: Q = It with t = 120 s.

Q = 0.25 × 120 = 30.0 C
23
Extended[2 marks]

Calculate the time for 450 C to pass when the current is 1.5 A.

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Method: t = Q ÷ I.

t = 450 ÷ 1.5 = 300 s
24
Extended[3 marks]

A phone battery delivers 0.80 A for 3.0 hours. Calculate the charge delivered.

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Method: t = 10 800 s.

Q = 0.80 × 10800 = 8640 C
25
Extended[2 marks]

State the direction of conventional current and of electron flow in a circuit.

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Method: Conventional + to −.

Conventional current flows from positive to negative; electrons flow from negative to positive
26
Extended[3 marks]

A current of 4.0 mA flows for 5.0 minutes. Calculate the charge.

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Method: Convert units.

Q = 0.0040 × 300 = 1.20 C
27
Extended[2 marks]

A charge of 6.0 C passes in 0.50 s. Calculate the current in mA.

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Method: I = Q/t.

I = 12 A = 12000 mA
28
Extended[2 marks]

Each electron carries 1.6 × 10⁻¹⁹ C. Calculate the number of electrons in 1.0 C.

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Method: n = Q ÷ e.

n = 1.0 ÷ 1.6×10⁻¹⁹ = 6.25 × 10¹⁸
29
Extended[3 marks]

A current of 2.0 A flows for 10 s. Using e = 1.6 × 10⁻¹⁹ C, calculate the number of electrons passing a point.

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Method: Q = 20 C.

n = 20 ÷ 1.6×10⁻¹⁹ = 1.25 × 10²⁰
30
Extended[2 marks]

Calculate the current when 90 C flows in 1.5 minutes.

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Method: t = 90 s.

I = 90 ÷ 90 = 1.00 A
31
Extended[2 marks]

A current of 5.0 A flows for 20 minutes. Calculate the charge.

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Method: t = 1200 s.

Q = 6000 C
32
Extended[3 marks]

A lightning strike transfers 25 C in 0.0010 s. Calculate the average current.

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Method: I = Q/t.

I = 25000 A
33
Extended[2 marks]

Calculate the time for 12 C to flow at 0.40 A.

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Method: t = Q/I.

t = 30.0 s
34
Extended[3 marks]

A battery is rated at 2000 mA h. Calculate the charge it can deliver in coulombs.

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Method: 2.0 A × 3600 s.

Q = 2.0 × 3600 = 7200 C
35
Extended[2 marks]

Explain why conventional current is said to flow from positive to negative.

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Method: Historical convention.

It was defined before electrons were discovered, assuming positive charge flowed
36
Extended[2 marks]

Electrons flow anticlockwise around a circuit. State the direction of conventional current.

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Method: Opposite.

Clockwise
37
Extended[3 marks]

A charge of 1800 C flows through a lamp in 1.0 hour. Calculate the current.

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Method: t = 3600 s.

I = 0.500 A
38
Extended[3 marks]

A current of 3.0 A flows. Calculate the number of electrons passing a point each second (e = 1.6 × 10⁻¹⁹ C).

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Method: n = I/e.

n = 1.88 × 10¹⁹
39
Extended[2 marks]

State the charge passing a point when 1 A flows for 1 s.

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Method: Definition.

1 coulomb
40
Extended[2 marks]

Explain why the current is the same in a series circuit in terms of charge per second.

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Method: Conservation.

The same amount of charge must pass each point per second because charge is conserved and cannot build up

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]

Explain why an ammeter must have a very low resistance and be connected in series, and what happens if it is wrongly connected in parallel with a lamp.

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Method: Short circuit.

It must not reduce the current it measures; in parallel its low resistance short-circuits the lamp, drawing a large current that may damage it
42
ChallengeCore[4 marks]

Compare a.c. and d.c., stating the source of each and sketching (describing) current–time graphs.

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Method: Graphs.

d.c. (cells): constant current in one direction, a horizontal line; a.c. (mains): current that reverses repeatedly, a sine-shaped curve crossing zero
43
ChallengeCore[3 marks]

Describe how electrons move through a metal wire when a current flows, and why the wire's free electrons do not run out.

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Method: Circuit loop.

Free electrons drift slowly through the lattice; they flow round a complete loop and are not used up
44
ChallengeCore[4 marks]

An analogue ammeter has two ranges: 0–1 A (50 divisions) and 0–5 A (50 divisions). Explain which range to use for a current of about 0.6 A and the reading precision on each.

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Method: Divisions.

Use 0–1 A: each division is 0.02 A; on 0–5 A each division is 0.1 A, less precise
45
ChallengeExtended[4 marks]

A capacitor discharges 0.050 C through a lamp in 2.5 ms. Calculate the average current and the number of electrons that flow (e = 1.6 × 10⁻¹⁹ C).

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Method: I = Q/t; n = Q/e.

I = 20.0 A; n = 3.13 × 10¹⁷
46
ChallengeExtended[4 marks]

A phone battery is rated 3000 mA h. It supplies an average of 250 mA. Calculate how long it lasts and the total charge delivered.

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Method: Hours = 3000/250.

12.0 h; Q = 3.0 × 3600 = 10800 C
47
ChallengeExtended[4 marks]

A current of 0.40 A flows for 15 minutes. Calculate the charge, then the time for the same charge to flow at 1.2 A.

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Method: Q = It.

Q = 360 C; t = 300 s
48
ChallengeExtended[3 marks]

Explain why electrons flow from the negative terminal to the positive terminal while conventional current is drawn the other way.

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Method: Convention.

Conventional current was defined as positive charge flow before electrons were discovered; electrons are negative so move the opposite way
49
ChallengeExtended[4 marks]

In 2.0 minutes, 1.5 × 10²⁰ electrons pass a point in a wire. Calculate the current.

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Method: Q = ne.

Q = 24.0 C; I = 24 ÷ 120 = 0.200 A
50
ChallengeExtended[4 marks]

A lightning flash carries 15 C in 0.20 ms. Calculate the average current and explain why such a short event can be so damaging.

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Method: I = Q/t.

I = 75000 A; the very large current transfers large amounts of energy in a tiny time
All IGCSE Physics topics← 4.2.1 Electric Charge4.2.3 Electromotive Force and Potential Difference →

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