IGCSE Physics: Efficiency and Sankey Diagrams | Edexcel Modular | Unit 3 | L2

IGCSE Physics: Efficiency and Sankey Diagrams | Edexcel Modular | Unit 3 | L2

This lesson covers spec points 3.4 and 3.5 — knowing and using the efficiency
equation, and describing energy transfers using Sankey diagrams.

PowerPoint includes:
• Retrieval starter reviewing energy stores and transfers from L1
• Direct Instruction (I Do) — efficiency defined as the proportion of input
energy usefully transferred; efficiency equation introduced in word and
symbol form; all three rearrangements modelled; Sankey diagrams introduced
with the key rule that arrow width is proportional to energy; worked example
with a light bulb Sankey diagram
• Guided Practice (We Do) — students draw Sankey diagrams for three devices
(electric motor, gas boiler, car engine) using gridded templates before
revealing the correct diagram; questions scaffold from reading values to
calculating efficiency to evaluating environmental impact
• Independent Practice (You Do) — activity sheet with exam-style questions
• Review and Reflect — MCQs and exit ticket

Activity Sheet includes:
• Formula box: efficiency = (useful output energy ÷ total input energy) × 100%
• 10 exam-style questions covering both directions of the efficiency calculation
(find efficiency, find useful output, find total input), Sankey diagram
interpretation, and an explanation of why 100% efficiency is impossible
• Contexts include LED lamps, wind turbines, petrol generators and hairdryers
• Full mark scheme for teacher use