Physics 0625 · syllabus 4.3
Cambridge IGCSE Physics 0625 — Electric circuits topical past papers
Circuit symbols and components, current and p.d. in series and parallel circuits, combined resistance, and potential dividers built with thermistors and LDRs.
- 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 Electric circuits covers
Circuit diagrams use standard symbols for cells and batteries, power supplies, switches, fixed and variable resistors, lamps, heaters, motors, bells, fuses, relays, ammeters, voltmeters, thermistors and light-dependent resistors (LDRs), and Extended candidates add diodes and light-emitting diodes (LEDs), which let current through in one direction only. An NTC thermistor's resistance falls as it gets warmer, and an LDR's resistance falls as the light on it gets brighter.
In a series circuit the current is the same at every point, the e.m.f.s of cells add, and the resistances add, R = R₁ + R₂. In a parallel circuit the source supplies more current than flows in any single branch, and two resistors in parallel have a smaller combined resistance than either alone. Household lamps are wired in parallel so that each gets the full supply voltage, can be switched on its own and keeps working if another fails. Extended candidates use three further rules — the currents into a junction add up to the currents out of it, because charge is conserved; the p.d.s across components in series add up to the supply p.d.; and parallel branches share the same p.d. — and work out the combined resistance of a pair of resistors in parallel.
For a fixed current, the component with the larger resistance has the larger p.d. across it. A potential divider puts this to work: two resistors in series share the supply p.d. in the ratio of their resistances, R₁/R₂ = V₁/V₂, which is Extended content. Make one of them a variable resistor, a thermistor or an LDR, and the output p.d. changes with the slider, the temperature or the light, which is how a circuit switches a heater on when a room cools or a lamp on when it gets dark.
In the syllabus
The headings this topic has in the Cambridge International 2026–2028 syllabus, as the board prints them.
- 4.3 Electric circuits
What you should be able to do
- Draw and read circuit diagrams with standard symbols, including diodes and LEDs (Extended)
- Add the e.m.f.s of cells and the resistances of resistors connected in series
- Describe how current behaves in series and parallel circuits, and explain why house lamps are wired in parallel
- Use the junction rule, add the p.d.s round a series circuit, and combine two resistors in parallel (Extended)
- Explain how the output of a potential divider changes as a thermistor warms, an LDR is lit or a slider moves
- Use R₁/R₂ = V₁/V₂ for a potential divider (Extended)
Key ideas
- Series: the same current everywhere; R = R₁ + R₂; the p.d.s add up to the supply p.d. (the last for Extended)
- Parallel: the same p.d. across each branch; the branch currents add up to the current from the source
- Two resistors in parallel: 1/R = 1/R₁ + 1/R₂, so R is less than either (the calculation for Extended)
- Potential divider: R₁/R₂ = V₁/V₂ (Extended)
- NTC thermistor: resistance falls as temperature rises; LDR: resistance falls as light intensity rises
How Electric circuits has been examined
From 2022 to 2026, Electric circuits 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 4.0 Ω resistor and a parallel pair of 6.0 Ω and 12 Ω resistors are joined in series across a 12 V battery. Find the total resistance, the current from the battery and the p.d. across the parallel pair.
- Parallel pair: 1/R = 1/6.0 + 1/12 = 3/12, so R = 4.0 Ω
- Total resistance = 4.0 + 4.0 = 8.0 Ω
- Current from the battery I = V/R = 12 / 8.0 = 1.5 A
- P.d. across the 4.0 Ω resistor = IR = 1.5 × 4.0 = 6.0 V, so the parallel pair has 12 − 6.0 = 6.0 V across it
- Check: 6.0 V drives 1.0 A through the 6.0 Ω resistor and 0.50 A through the 12 Ω resistor, which add up to 1.5 A
Answer: Total resistance 8.0 Ω; current 1.5 A; 6.0 V across the parallel pair
Written by Momentum for this page, with its own numbers; it is not taken from a past paper.
Mistakes that cost marks
- Adding parallel resistances as if they were in series — two 6.0 Ω resistors in parallel make 3.0 Ω, not 12 Ω, and a parallel pair is always less than the smaller resistor
- Forgetting the last step of 1/R = 1/R₁ + 1/R₂ — for 4.0 Ω and 12 Ω, 1/R = 1/3.0, so R = 3.0 Ω, not 0.33 Ω
- Saying current is used up round a series circuit — the current is the same at every point; it is energy that is transferred, not charge
- Getting a potential divider's change backwards — when an LDR is lit its resistance falls, so its share of the p.d. falls and the p.d. across the fixed resistor rises
- Expecting current through a diode drawn the wrong way round — a diode conducts only in the direction its arrow points
Exam technique
- Explain a potential divider as a chain: the condition changes, the sensor's resistance changes, its share of the supply p.d. changes, so the output changes
- Label the current in each branch on the diagram before calculating, and check that the branch currents add up to the total
- In parallel-resistance working, write the formula, substitute, and take the reciprocal on a separate line
- Draw symbols neatly and join them with straight lines and no gaps, because unclear symbols lose marks
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.