Free GCSE Physics lesson: Energy Stores
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Free Lessons -> GCSE / Key Stage 4 -> Physics -> Energy Stores

Lesson 2 · GCSE / Key Stage 4 · Physics

Energy stores and transfers

Learn how GCSE Physics describes energy stores, transfer pathways, conservation and wasted energy.

Qualification: GCSE Subject: Physics Energy

Energy

Lesson overview

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

FocusEnergy stores and transfers
Time45-60 minutes
EquipmentCalculator and a list of common energy stores.
Practical linkNo separate practical method focus
Maths tagsM1 substitution with units, M6 ratio and percentage, M8 multi-step calculations

What you will learn

  • Name common energy stores and transfer pathways.
  • Explain conservation of energy without saying energy disappears.
  • Calculate efficiency from useful and total energy transfer.
  • Describe dissipated energy in clear exam language.

Energy scenario bank

Use the phone, kettle, braking bicycle and falling ball scenarios below to practise naming the starting store, useful transfer and dissipated transfer.

Energy stores and transfers infographic

Infographic explaining energy stores and transfers, including transfer pathways, conservation, dissipation and useful energy.
Use this visual to track where energy starts, where it transfers and where it is dissipated.Download visual

Clear explanation

GCSE Physics does not treat energy as a substance that gets used up. Energy is stored in different ways and transferred between stores.

Useful transfer is the part that helps the device or process do its job. Dissipated energy is still conserved, but it spreads to less useful stores, often the thermal store of the surroundings.

Efficiency compares useful output with total input. It can be written as a decimal or percentage.

Key diagram

Sankey diagram for useful and dissipated energy A Sankey diagram shows one hundred joules of input energy splitting into seventy joules useful output and thirty joules dissipated to the surroundings. 100 J input 70 J useful 30 J dissipated
Diagram: the arrow widths show energy is conserved while some energy is transferred usefully and some is dissipated.

Worked examples

Kettle energy transfer

A kettle transfers 180 000 J electrically. 150 000 J is transferred usefully to the thermal store of the water.

Efficiency = useful energy output ÷ total energy input

Efficiency = 150 000 ÷ 180 000 = 0.833...

Answer: The efficiency is about 0.83, or 83% to the nearest percent.

Quick checks

Choose an answer, then check your thinking.

1. A hot drink cools down on a desk. Where is energy mainly transferred?

2. A motor has 200 J input and 80 J useful output. What is its efficiency?

Practice questions

Question 1

A battery-powered torch transfers energy from which starting store?

Reveal answer and marking guidance

Answer: The chemical store of the battery.

Marking: Credit chemical store, with useful transfer by light and wasted transfer to thermal stores.

Question 2

A machine transfers 500 J in and 125 J usefully out. Calculate the efficiency as a percentage.

Reveal answer and marking guidance

Answer: 25%.

Marking: Credit 125 ÷ 500 = 0.25 and converting to 25%.

Question 3

A bicycle brake makes the wheel warmer. Explain the energy transfer.

Reveal answer and marking guidance

Answer: Kinetic energy is transferred mechanically and then to thermal stores of the brake, wheel and surroundings.

Marking: Credit kinetic store decreasing and thermal stores increasing.

Question 4

Why is 'energy is wasted' acceptable only if you explain what wasted means?

Reveal answer and marking guidance

Answer: Because the energy is not destroyed; it is dissipated to less useful stores, usually heating the surroundings.

Marking: Credit conservation plus the idea of less useful spreading.

Practice ladder

FluencyRecall the key definition, unit, equation or model before using the lesson questions.
ApplicationApply energy stores and transfers 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

  • Saying energy is used up rather than transferred or dissipated.
  • Confusing a store, such as chemical, with a pathway, such as electrical.
  • Dividing total input by useful output when calculating efficiency.
  • Forgetting to convert a decimal efficiency into a percentage when asked.

Extension challenge

Draw a simple Sankey diagram for a kettle, then label useful energy and dissipated energy with approximate values.

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 energy stores and transfers.

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 Forces and Motion Basics.

Previous lesson: Getting StartedBack to GCSE Physics lessonsNext lesson: Forces and Motion Basics