Who this is for: Cambridge IGCSE Physics (0625) students who want electric circuits — series and parallel layouts, symbols and sensor components — to become reliable marks instead of wire-following without circuit logic.
What query it owns: how to understand and revise electric circuits in Cambridge IGCSE Physics.
Why this is safe: this page owns the electric circuits revision-guide angle, while Tutopiya’s Electric Circuits subtopic page owns the learning resource and the free quiz owns the practice.

Electric circuits are tested heavily in Cambridge IGCSE Physics (0625) through diagram reading, circuit construction and component behaviour. Examiners expect you to know standard symbols, predict how current and p.d. behave in series and parallel, and explain how LDRs and thermistors change resistance in real applications. This guide covers the syllabus content and the question types that appear every year.

Key takeaways

• Series: one path for current; same current everywhere; p.d. shared; R_total = R₁ + R₂.
• Parallel: multiple branches; same p.d. across each branch; current splits; 1/R = 1/R₁ + 1/R₂.
• LDR: resistance decreases in brighter light — used in automatic outdoor lights.
• Thermistor (NTC): resistance decreases as temperature increases — used in temperature sensors.
• Potential divider: two resistors in series; p.d. splits in proportion to resistance.

What are electric circuits in Cambridge IGCSE Physics?

An electric circuit is a closed path through which charge can flow. Components are connected in series (one after another) or in parallel (side by side). In Cambridge IGCSE Physics (0625) you must draw and interpret circuit diagrams using standard symbols, calculate combined resistance, and describe how variable resistors and sensors respond to environmental changes.

You can read the full explanation, worked examples and notes on Tutopiya’s Electric Circuits subtopic page before you attempt questions.

The core ideas you must master

Idea	What it means	How the exam uses it
Circuit symbols	Cell, battery, resistor, lamp, switch, LDR, thermistor, diode	”Draw the symbol for an LDR.”
Series current	Same I through all components	”State the current through each lamp.”
Parallel p.d.	Same V across branches	”State the p.d. across the parallel branch.”
LDR behaviour	Light ↑ → R ↓ → I ↑ (in simple circuit)	“Explain how a night light switches on.”
Thermistor behaviour	Temperature ↑ → R ↓	“Explain the thermistor’s role in a fire alarm.”

Series vs parallel circuits: what changes when you rewire?

Feature	Series	Parallel
Current	Same everywhere	Divides between branches
Potential difference	Shared (adds to source e.m.f.)	Same across each branch
Total resistance	Increases (sum)	Decreases (combined < smallest)
If one component breaks	Circuit open — all stop	Other branches may continue
Domestic wiring	Rare for appliances	Standard for mains at home

How to analyse a circuit diagram — step by step

1. Identify series and parallel sections — trace one complete loop at a time.
2. Label what is equal — series: same I; parallel: same V per branch.
3. Calculate combined resistance for each section before finding total.
4. Apply V = IR to find unknown currents or p.d.s.
5. For sensors, state how resistance change affects current in context.

Once you have worked through a few, test yourself with the free Electric Circuits quiz.

Electric circuits in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical circuits stem
Draw / Sketch	Circuit diagram with symbols	”Draw a circuit with an LDR and a lamp in series.”
Calculate	Combined R, I or V	”Calculate the total resistance of the circuit.”
Explain	Cause and effect	”Explain why the lamp brightens when light falls on the LDR.”
State	Short factual answer	”State one advantage of parallel wiring at home.”
Suggest	Apply to a scenario	”Suggest how a thermistor could detect a temperature rise.”

Worked exam-style stems (how to answer the wording)

1. “Two resistors, 6 Ω and 3 Ω, are connected in parallel. Calculate the combined resistance.” 1/R = 1/6 + 1/3 = 1/6 + 2/6 = 3/6 = 1/2 → R = 2 Ω. Mark-scheme reward: reciprocal method shown.
2. “An LDR is in series with a lamp. Explain what happens when the light intensity increases.” Light intensity ↑ → LDR resistance decreases → total circuit resistance decreases → current increases → lamp gets brighter. Reward: resistance change linked to current and brightness.
3. “State one reason why appliances in a house are connected in parallel.” Each appliance receives the full mains voltage / if one appliance fails, others keep working. Reward: either valid advantage.

When you can recognise the wording instantly, work through the Electric Circuits quiz to lock the circuit rules in.

How electric circuits connect to the rest of the syllabus

Circuits build on Electrical Quantities — V = IR and P = VI. Safety applications appear in Electrical Safety. Electromagnets link back to Simple Phenomena of Magnetism. The Cambridge IGCSE Physics resource hub links every Electricity and Magnetism subtopic.

Common mistakes students make

• Drawing parallel lamps but analysing them as series for current.
• Stating LDR resistance increases in bright light (it decreases).
• Adding parallel resistances directly (6 + 3 ≠ combined parallel resistance).
• Placing ammeters in parallel (ammeters must be in series).
• Forgetting that a diode allows current in one direction only.

When you need more support

If circuit analysis keeps costing marks — especially combined resistance and sensor explain chains — work through the Electric Circuits quiz, then get focused help from a Cambridge IGCSE Physics tutor.

Frequently asked questions

Is circuit analysis hard in Cambridge IGCSE Physics? The rules are fixed — learn series vs parallel once, then apply V = IR systematically.

What does an LDR do? Its resistance decreases when light intensity increases; used in automatic lighting circuits.

Why are home appliances wired in parallel? Each gets full mains voltage and can be switched independently; one failure does not break the whole system.

How do I revise electric circuits effectively? Practise drawing symbols, solve combined resistance problems, explain LDR/thermistor chains, then take the Electric Circuits quiz.

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