IGCSE Physics: Transformers | Magnetism & Electromagnetism | Edexcel Modular | Unit 7 | L8

IGCSE Physics: Transformers | Magnetism & Electromagnetism | Edexcel Modular | Unit 7 | L8

This lesson covers spec points 7.17P–7.20P (Physics only) of the Edexcel Modular IGCSE Physics specification — transformer structure, the turns
ratio equation, power conservation in an ideal transformer, and the role of transformers in
the National Grid.

PowerPoint includes:
• Retrieval starter reviewing electromagnetic induction and generators from L7
• Direct Instruction (I Do) — transformer structure explained (primary coil, secondary coil,
soft iron core); why only AC works established (changing field in core induces voltage in
secondary; DC produces a static field with no induction); step-up and step-down transformers
contrasted using turns ratio; turns ratio equation introduced (Vp/Vs = Np/Ns); power
conservation introduced (VpIp = VsIs for 100% efficiency); National Grid explained —
step-up at power station increases voltage and reduces current, reducing energy lost as heat
in cables; step-down near consumers reduces voltage to safe levels
• Direct Instruction worked examples — three I Do calculations with full step-by-step working:
(1) find secondary voltage given turns and primary voltage; (2) find number of secondary
turns given both voltages and primary turns; (3) find secondary current given both voltages
and primary current
• Guided Practice (We Do) — three matching calculations, one of each type: find secondary
voltage; find primary turns; find secondary current; answers revealed after each
• Check for Understanding — 4 MCQs including a true/false on DC transformers
• Independent Practice (You Do) — activity sheet with exam-style questions
• Review and Reflect — exit ticket: what would happen if the National Grid were switched
to direct current?

Activity Sheet includes:
• Formula boxes for both transformer equations: Vp/Vs = Np/Ns and VpIp = VsIs
• 9 questions covering transformer structure, AC-only explanation, step-up/step-down
identification, turns ratio calculations and National Grid explanation (22 marks)
• Stretch question: a power station generates at 25 000 V with a current of 800 A; a
step-up transformer raises this to 400 000 V — state whether the transformer has more
turns on the primary or secondary and justify; calculate the transmission current;
explain qualitatively why high-voltage transmission reduces energy loss in cables
• Note: P = I²R does not appear anywhere in this resource — National Grid questions use
qualitative reasoning only, consistent with the Edexcel Modular specification
• Physics-only footer on all pages
• Full mark scheme for teacher use