Free GCSE Physics lesson: I-V Characteristics
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Free Lessons -> GCSE / Key Stage 4 -> Physics -> I-V Characteristics

Lesson 19 · GCSE / Key Stage 4 · Physics

Required practical: I-V characteristics

Investigate current-potential difference graphs for a resistor, filament lamp and diode.

Qualification: GCSE Subject: Physics Required practical Separate Physics and Combined Science

Practical skills

This lesson builds i-v characteristics practical and graph interpretation for GCSE Physics.

Use the core lesson first, then match the exam-board guidance to your school route. Many pupils meet this content through Combined Science as well as Separate Physics.

Good forSeparate Physics and Combined Science
FocusI-V characteristics practical and graph interpretation
Time45-60 minutes
EquipmentPower supply, variable resistor, ammeter, voltmeter, resistor, filament lamp, diode and leads.
Paper fitSupports both papers through study, maths or practical skills
TierFoundation and Higher core
Practical linkRequired/core practical focus
Maths tagsM1 units and equation sense

What you will learn

  • Describe how to measure current and potential difference for a component.
  • Explain why a variable resistor is used.
  • Interpret I-V graphs for an ohmic resistor, filament lamp and diode.
  • Link graph shape to changing resistance.

Exam-board fit

RouteSeparate Physics and Combined Science
PaperSupports both papers through study, maths or practical skills
TierFoundation and Higher core
Specification fitPractical skills: I-V characteristics practical and graph interpretation
Practical linkRequired/core practical focus
Maths ladderM1 units and equation sense

Exact paper labels and specification-point numbering vary by board and cohort, so match this lesson to your school route before using past-paper questions.

I-V graph prompts supplied on this page

Use the resistor, lamp and diode descriptions to practise matching graph shape to component behaviour.

Clear explanation

An I-V practical measures the current through a component for different potential differences across it. The ammeter is in series and the voltmeter is in parallel with the component.

An ohmic resistor gives a straight-line graph through the origin at constant temperature. A filament lamp curves because the filament heats up and resistance increases.

A diode allows current mainly in one direction, so its graph shows very small current in reverse bias and a sharp increase in forward bias after a threshold.

Key graph

I-V characteristic graph shapes An I-V graph shows a straight ohmic resistor line through the origin, a filament lamp curve that flattens at higher potential difference and a diode curve with little reverse current and sharp forward current. potential difference / V current / A resistor lamp diode
Graph: each component has a distinct graph shape, so pupils can compare behaviour rather than imagine the graph.

Key diagram

I-V characteristics circuit with variable resistor and meters A component circuit shows an ammeter in series, a voltmeter in parallel across the test component and a variable resistor to change potential difference. A test V variable resistor
Diagram: the apparatus layout makes clear how potential difference is varied and how current and voltage are measured.

Worked examples

Identifying a filament lamp graph

The graph starts steep, then becomes less steep as potential difference increases.

Current still increases, but not in direct proportion.

The filament gets hotter.

Answer: This is a filament lamp because its resistance increases as temperature rises.

Quick checks

Choose an answer, then check your thinking.

1. Where should the voltmeter be connected?

2. Which component has an I-V graph that is straight through the origin at constant temperature?

Practice questions

Question 1

Why is an ammeter connected in series?

Reveal answer and marking guidance

Answer: So the current through the component also passes through the ammeter.

Marking: Credit same current in series.

Question 2

Why does a filament lamp's resistance increase?

Reveal answer and marking guidance

Answer: The filament gets hotter, so ions vibrate more and oppose electron flow more.

Marking: Credit heating and increased lattice vibrations.

Question 3

What does a diode do in reverse bias?

Reveal answer and marking guidance

Answer: It allows little or no current to flow.

Marking: Credit one-way conduction idea.

Question 4

Why should readings be taken for positive and negative potential differences?

Reveal answer and marking guidance

Answer: To see whether the component behaves the same in both directions.

Marking: Credit checking symmetry or diode direction behaviour.

Exam practice ladder

AO1 fluencyRecall the key definition, unit, equation or model before using the lesson questions.
AO2 applicationApply i-v characteristics practical and graph interpretation to an unfamiliar device, practical setup or data description.
AO3 analysisUse evidence, graph features, uncertainty, method quality or conclusion wording where the question asks you to evaluate.
Maths skillM1 units and equation sense

Answers and marking guidance

The exact practice answers are hidden under each question so you can try first. For this lesson, marks come from using the correct physics model, choosing the right equation where needed, keeping units with values, and explaining changes with precise words such as transfer, resultant force, acceleration, evidence and uncertainty.

Common mistakes

  • Putting the voltmeter in series.
  • Calling every curved graph a diode.
  • Ignoring heating in the filament lamp.
  • Changing the circuit while the power supply is on without care.

Exam-board guidance

All supported routes assess the core physics idea, but they may group topics, practicals and paper wording differently.

AQA GCSE Physics

AQA GCSE Physics: use this lesson for i-v characteristics practical and graph interpretation, then check whether your class is taking Separate Physics or Combined Science.

OCR GCSE Physics

OCR GCSE Physics: the core physics idea is shared, but Gateway and Twenty First Century may organise questions differently.

Pearson Edexcel GCSE Physics

Pearson Edexcel GCSE Physics: practise the concept, the equation use and the practical language because questions often connect them.

Eduqas GCSE Physics

Eduqas GCSE Physics: learn the core explanation and practise applying it to unfamiliar contexts, data and practical questions.

WJEC Wales

WJEC Wales: check whether your class is using the current GCSE Physics route or a newer science route, then use this lesson for the shared physics idea.

CCEA GCSE Physics

CCEA GCSE Physics: connect the idea to your unit and remember that practical skills are assessed directly.

Extension challenge

Sketch the three I-V graphs and annotate the physical reason for each shape.

Reveal answer

Example answer: A strong extension response names the physics model, uses accurate units and explains why the evidence supports the conclusion.

Next lesson

Next, continue with Required Practical: Resistance of a Wire.

Previous lesson: Specific Heat PracticalBack to GCSE Physics lessonsNext lesson: Required Practical: Resistance of a Wire