Free GCSE Physics lesson: Resistance of a Wire
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Free Lessons -> GCSE / Key Stage 4 -> Physics -> Resistance of a Wire

Lesson 20 · GCSE / Key Stage 4 · Physics

Practical method: resistance of a wire

Investigate how wire length affects resistance while controlling material, thickness and temperature.

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.

FocusResistance of a wire practical
Time45-60 minutes
EquipmentResistance wire, metre ruler, crocodile clips, ammeter, voltmeter, power supply and switch.
Practical linkRequired/core practical focus
Maths tagsM1 substitution with units

What you will learn

  • Describe how to measure resistance for different wire lengths.
  • Explain why current should be kept low or switched off between readings.
  • Identify control variables for a fair test.
  • Use R = V divided by I to calculate resistance.

Wire investigation data supplied on this page

Use the wire length and V-I data to practise calculating resistance and explaining fair testing.

Resistance of a wire practical infographic

Infographic explaining the GCSE Physics resistance of a wire practical, including circuit meter placement, wire length, resistance equals potential difference divided by current, control variables, a resistance-length graph and exam checks.
Use this visual to set up the resistance wire practical, calculate resistance and link wire length to graph evidence.Download visual

Clear explanation

Longer wires usually have greater resistance because electrons collide with more ions as they move through the wire.

To investigate length fairly, keep the material and diameter of the wire the same. Temperature should also be controlled because heating changes resistance.

Measure potential difference across the wire and current through it, then calculate resistance using R = V ÷ I for each length.

Key graph

Resistance against wire length graph A resistance against wire length graph rises in a straight line, showing resistance increases as the same wire gets longer. wire length / cm resistance / ohms longer wire, larger resistance
Graph: the axes show resistance against length and the straight trend matches the same wire material and thickness.

Key diagram

Resistance of a wire practical apparatus A resistance wire is stretched along a ruler with crocodile clips setting length, while an ammeter and voltmeter measure the circuit. A V change clip separation to change wire length
Diagram: the ruler and clip positions show exactly what length is varied while resistance is measured.

Worked examples

Calculating resistance

A wire has 1.5 V across it and current 0.30 A.

R = V ÷ I

R = 1.5 ÷ 0.30 = 5

Answer: The resistance is 5 ohms.

Quick checks

Choose an answer, then check your thinking.

1. What is the independent variable in the wire-length investigation?

2. Why should the wire not get too hot?

Practice questions

Question 1

A wire has 2.4 V across it and 0.40 A through it. Calculate resistance.

Reveal answer and marking guidance

Answer: 6 ohms.

Marking: Credit R = V ÷ I and 2.4 ÷ 0.40 = 6 ohms.

Question 2

Name two control variables in this practical.

Reveal answer and marking guidance

Answer: Wire material and wire diameter.

Marking: Credit material, thickness/diameter and temperature.

Question 3

Why use a switch in the circuit?

Reveal answer and marking guidance

Answer: To turn current off between readings and reduce heating.

Marking: Credit reducing heating and keeping temperature controlled.

Question 4

What graph would show how resistance changes with length?

Reveal answer and marking guidance

Answer: Resistance on the vertical axis against length on the horizontal axis.

Marking: Credit resistance vs length with correct axes.

Practice ladder

FluencyRecall the key definition, unit, equation or model before using the lesson questions.
ApplicationApply resistance of a wire practical 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 substitution with units

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

  • Changing wire material as well as length.
  • Leaving current on so the wire heats up.
  • Calculating resistance as current divided by voltage.
  • Moving crocodile clips without recording the exact length.

Extension challenge

Predict and explain the graph shape for resistance against length for the same type of wire.

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 resistance of a wire practical.

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: Force and Acceleration.

Previous lesson: I-V CharacteristicsBack to GCSE Physics lessonsNext lesson: Practical: Force and Acceleration