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

Practical method: I-V characteristics

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

Qualification: GCSE Subject: Physics Practical method

Practical skills

Lesson overview

This lesson introduces the core physics idea, the useful equipment and the calculation or data skills used on this page.

FocusI-V characteristics practical and graph interpretation
Time45-60 minutes
EquipmentPower supply, variable resistor, ammeter, voltmeter, resistor, filament lamp, diode and leads.
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.

I-V graph prompts supplied on this page

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

I-V characteristics practical infographic

Infographic explaining the GCSE Physics I-V characteristics practical, including meter placement, variable resistor method, V equals I R, variables, graph shapes for an ohmic resistor, filament lamp and diode, and exam checks.
Use this visual to set up the I-V practical, read graph shapes and avoid meter-placement misconceptions.Download visual

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.

Practice ladder

FluencyRecall the key definition, unit, equation or model before using the lesson questions.
ApplicationApply i-v characteristics practical and graph interpretation to an unfamiliar device, practical setup or data description.
Practical interpretationUse 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.

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.

Exam-board guidance

Short board notes only. Learn the core physics above first.

AQA GCSE Physics

AQA GCSE Physics: often rewards clear physics explanations, correct equations, units and practical evidence for i-v characteristics practical and graph interpretation.

OCR GCSE Physics

OCR GCSE Physics: often values precise definitions, clear working, graph interpretation and links between models and evidence.

Pearson Edexcel GCSE Physics

Pearson Edexcel GCSE Physics: often combines the concept with equation use, data handling and practical interpretation.

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: often expects accurate terms, units and evidence-based explanations using the shared physics idea.

CCEA GCSE Physics

CCEA GCSE Physics: connect the idea to your current unit and use the same practical method language your class uses.

Next lesson

Next, continue with Practical: Resistance of a Wire.

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