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

Required practical: resistance of a wire

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

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

Practical skills

This lesson builds resistance of a wire practical 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
FocusResistance of a wire practical
Time45-60 minutes
EquipmentResistance wire, metre ruler, crocodile clips, ammeter, voltmeter, power supply and switch.
Paper fitSupports both papers through study, maths or practical skills
TierFoundation and Higher core
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.

Exam-board fit

RouteSeparate Physics and Combined Science
PaperSupports both papers through study, maths or practical skills
TierFoundation and Higher core
Specification fitPractical skills: Resistance of a wire practical
Practical linkRequired/core practical focus
Maths ladderM1 substitution with units

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.

Wire investigation data supplied on this page

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

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.

Exam practice ladder

AO1 fluencyRecall the key definition, unit, equation or model before using the lesson questions.
AO2 applicationApply resistance of a wire practical 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 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.

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 resistance of a wire practical, 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

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.

Next lesson

Next, continue with Required Practical: Force and Acceleration.

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