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

Lesson 42 · GCSE / Key Stage 4 · Physics

Transformer calculations and efficiency

Use transformer turns ratios, power relationships and efficiency ideas in National Grid questions.

Qualification: GCSE Subject: Physics Transformers Separate Physics and Combined Science where transformer calculations are taught

Electricity

This lesson builds transformer equations, power and efficiency 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 where transformer calculations are taught
FocusTransformer equations, power and efficiency
Time45-60 minutes
EquipmentCalculator and transformer equation sheet if used by your course.
Paper fitPaper 1 focus on most GCSE Physics routes
TierFoundation and Higher core
Practical linkNo required practical focus
Maths tagsM1 substitution with units, M2 rearranging/equations, M6 ratio and percentage

What you will learn

  • Use the transformer turns ratio equation.
  • Explain step-up and step-down behaviour using coil turns.
  • Use input and output power for ideal transformers.
  • Explain efficiency limits and heating losses.

Exam-board fit

RouteSeparate Physics and Combined Science where transformer calculations are taught
PaperPaper 1 focus on most GCSE Physics routes
TierFoundation and Higher core
Specification fitElectricity: Transformer equations, power and efficiency
Practical linkNo required practical focus
Maths ladderM1 substitution with units, M2 rearranging/equations, M6 ratio and percentage

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.

Transformer calculation set supplied on this page

Use the primary coil, secondary coil and power-transfer examples to practise turns-ratio calculations.

Clear explanation

In a transformer, the ratio of potential differences equals the ratio of turns on the coils. More turns on the secondary coil means a higher output potential difference.

An ideal transformer transfers power without loss, so input power equals output power. Real transformers waste some energy by heating.

Step-up transformers increase potential difference and reduce current for the same transmitted power. This helps reduce heating losses in cables.

Key diagram

Transformer coils with different numbers of turns A transformer core has a primary coil with fewer turns and a secondary coil with more turns, labelled with input and output potential difference. primary secondary fewer turns more turns turns ratio links input p.d. to output p.d.
Diagram: the different coil counts make the voltage ratio model visible before pupils use the transformer equation.

Worked examples

Turns ratio

A transformer has 100 turns on the primary coil and 500 turns on the secondary coil.

The secondary has five times as many turns.

The secondary potential difference is five times the primary potential difference.

Answer: If the primary is 20 V, the secondary is 100 V.

Quick checks

Choose an answer, then check your thinking.

1. What kind of transformer has more secondary turns than primary turns?

2. In an ideal transformer, what happens to input and output power?

Practice questions

Question 1

A transformer has 200 primary turns and 1000 secondary turns. Is it step-up or step-down?

Reveal answer and marking guidance

Answer: Step-up.

Marking: Credit more secondary turns than primary turns.

Question 2

A transformer has 50 V on the primary and twice as many secondary turns as primary turns. What is the secondary potential difference?

Reveal answer and marking guidance

Answer: 100 V.

Marking: Credit doubling potential difference.

Question 3

An ideal transformer outputs 60 W. What is its input power?

Reveal answer and marking guidance

Answer: 60 W.

Marking: Credit ideal transformer power conservation.

Question 4

Why are real transformers less than 100% efficient?

Reveal answer and marking guidance

Answer: Some energy is dissipated, mainly by heating in coils and core.

Marking: Credit heating losses or energy transferred to thermal stores.

Exam practice ladder

AO1 fluencyRecall the key definition, unit, equation or model before using the lesson questions.
AO2 applicationApply transformer equations, power and efficiency 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

  • Reversing primary and secondary turns.
  • Assuming real transformers are perfectly efficient.
  • Saying step-up means current also increases for the same power.
  • 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 transformer equations, power and efficiency, 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

Explain why stepping up voltage for transmission can reduce cable heating even when the same power is delivered.

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: Infrared Radiation.

Previous lesson: Terminal VelocityBack to GCSE Physics lessonsNext lesson: Required Practical: Infrared Radiation