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

Lesson 37 · GCSE / Key Stage 4 · Physics

Transformers and the National Grid

Explain step-up and step-down transformers, transmission voltage and energy losses in the National Grid.

Qualification: GCSE Subject: Physics Grid Separate Physics and Combined Science

Electricity

This lesson builds transformers and electricity transmission 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
FocusTransformers and electricity transmission
Time45-60 minutes
EquipmentCalculator and transformer equation practice.
Paper fitPaper 1 focus on most GCSE Physics routes
TierFoundation and Higher core
Practical linkNo required practical focus
Maths tagsM1 units and equation sense

What you will learn

  • Explain why the National Grid uses high potential difference.
  • Distinguish step-up and step-down transformers.
  • Use the transformer turns ratio equation where required.
  • Explain why lower current reduces heating losses.

Exam-board fit

RouteSeparate Physics and Combined Science
PaperPaper 1 focus on most GCSE Physics routes
TierFoundation and Higher core
Specification fitElectricity: Transformers and electricity transmission
Practical linkNo required practical focus
Maths ladderM1 units and equation sense

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.

Grid examples supplied on this page

Use the power station, pylon and home supply examples to practise transformer and transmission reasoning.

Clear explanation

The National Grid transfers electrical power from power stations to consumers. High potential difference is used for transmission because it allows lower current for the same power.

Lower current reduces heating losses in cables. Step-up transformers increase potential difference before transmission; step-down transformers reduce it before homes and businesses.

Transformers work with alternating current because changing magnetic fields are needed for induction between coils.

Key diagram

National Grid step-up and step-down transformer route A power station connects to a step-up transformer, high-voltage transmission cables and a step-down transformer before homes. station step-up high p.d., low current step-down
Diagram: the route shows why voltage is raised for transmission and lowered before use in homes.

Worked examples

Why step up voltage?

The same power can be transmitted at high potential difference and low current.

Heating loss depends strongly on current.

Reducing current reduces wasted energy in cables.

Answer: Step-up transformers reduce transmission losses by allowing lower current.

Quick checks

Choose an answer, then check your thinking.

1. What does a step-up transformer do?

2. Why is high potential difference useful for long-distance transmission?

Practice questions

Question 1

Name the transformer used before long-distance transmission.

Reveal answer and marking guidance

Answer: Step-up transformer.

Marking: Credit step-up because potential difference is increased.

Question 2

Name the transformer used before electricity enters homes.

Reveal answer and marking guidance

Answer: Step-down transformer.

Marking: Credit step-down because potential difference is reduced for safer use.

Question 3

Explain why lower current reduces wasted energy in transmission cables.

Reveal answer and marking guidance

Answer: Less energy is transferred to the thermal stores of the cables due to resistance.

Marking: Credit reduced heating losses in cables.

Question 4

Why do transformers require alternating current?

Reveal answer and marking guidance

Answer: A changing current produces a changing magnetic field, which induces potential difference in the secondary coil.

Marking: Credit changing magnetic field and induction.

Exam practice ladder

AO1 fluencyRecall the key definition, unit, equation or model before using the lesson questions.
AO2 applicationApply transformers and electricity transmission 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 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

  • Saying high voltage is used because it increases current.
  • Confusing step-up and step-down roles.
  • Ignoring heating losses in cables.
  • Forgetting transformers need alternating current.

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 transformers and electricity transmission, 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

Describe the full route from power station generator to home socket, naming the transformer type at each stage.

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 Space Physics: Solar System and Orbits.

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