Free GCSE Physics lesson: Infrared Practical
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Free Lessons -> GCSE / Key Stage 4 -> Physics -> Infrared Practical

Lesson 43 · GCSE / Key Stage 4 · Physics

Practical method: infrared radiation

Investigate how surface colour and texture affect infrared emission and absorption.

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.

FocusInfrared radiation practical method and evaluation
Time45-60 minutes
EquipmentLeslie cube or surface samples, thermometer or infrared detector and stopwatch.
Practical linkRequired/core practical focus
Maths tagsM1 units and equation sense

What you will learn

  • Describe how to compare infrared emission from different surfaces.
  • Identify independent, dependent and control variables.
  • Explain why matt black surfaces are strong emitters and absorbers.
  • Evaluate reliability and safety in thermal radiation practicals.

Infrared practical prompts supplied on this page

Use the Leslie cube and surface-card examples to practise method, variables and evaluation wording.

Infrared radiation practical infographic

Infographic explaining the GCSE Physics infrared radiation practical, including a Leslie cube or metal containers, matt black, white and shiny silver surfaces, detector distance controls, variables, method steps, graph evidence and common misconceptions.
Use this visual to set up the infrared radiation practical, control distance and compare emission from different surface finishes.Download visual

Clear explanation

Infrared radiation transfers energy by electromagnetic waves. All warm objects emit infrared radiation, but different surfaces emit and absorb different amounts.

A typical investigation compares surfaces such as matt black, shiny silver, white and dull metal while keeping temperature, distance and detector position controlled.

Matt black surfaces are usually the best emitters and absorbers. Shiny light surfaces are usually poor emitters and absorbers but good reflectors.

Worked examples

Fair comparison of surfaces

A detector is placed the same distance from each side of a Leslie cube.

The cube is filled with hot water at the same temperature for each side.

The detector reading is compared for each surface.

Answer: Distance, temperature and detector angle are controlled so surface type is the independent variable.

Quick checks

Choose an answer, then check your thinking.

1. Which surface is usually the best infrared emitter?

2. What variable should be kept the same when comparing surfaces?

Practice questions

Question 1

Name the independent variable in an investigation comparing matt black and shiny silver surfaces.

Reveal answer and marking guidance

Answer: Surface type or surface finish.

Marking: Credit surface colour/texture.

Question 2

Name one control variable in a Leslie cube investigation.

Reveal answer and marking guidance

Answer: Distance from detector, temperature of the cube, detector angle or room conditions.

Marking: Credit a variable that affects infrared reading.

Question 3

Why should hot water be handled carefully?

Reveal answer and marking guidance

Answer: It can burn or scald, so eye protection and careful handling are needed.

Marking: Credit sensible thermal safety.

Question 4

Why might repeated readings improve the investigation?

Reveal answer and marking guidance

Answer: They help identify anomalies and support a more reliable mean.

Marking: Credit reliability and anomalies.

Practice ladder

FluencyRecall the key definition, unit, equation or model before using the lesson questions.
ApplicationApply infrared radiation practical method and evaluation 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

  • Changing detector distance between surfaces.
  • Saying shiny silver is always the best emitter.
  • Ignoring the starting temperature of the surface.
  • Writing a conclusion without linking to evidence.

Extension challenge

Design a table for a Leslie cube investigation, including repeats and a mean detector reading for each surface.

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 infrared radiation practical method and evaluation.

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 Sound, Ultrasound and Seismic Waves.

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