This deep dive covers Sankey Diagrams within Efficiency for GCSE Physics. Revise Efficiency in Energy for GCSE Physics with 19 exam-style questions and 4 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 3 of 13 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
🔄 Sankey Diagrams
A Sankey diagram is a visual tool for showing energy transfers. The width of each arrow is proportional to the amount of energy it represents.
- A single thick arrow on the left represents total input energy
- An arrow pointing to the right represents useful output energy
- Arrows pointing downward (or in other directions) represent wasted energy
- The total width of all output arrows must equal the width of the input arrow (conservation of energy)
For example, a car engine with 25% efficiency would have a Sankey diagram where 25% of the arrow width points to "kinetic energy" and 75% points downward to "thermal energy" (heat from combustion and friction).
Sankey diagrams are useful because you can see at a glance how much energy is wasted relative to the useful output — the bigger the downward arrows, the less efficient the device.
Practice questions for Efficiency
Which equation correctly defines efficiency?
Explain one method that can be used to reduce unwanted energy transfers in a machine and state how it reduces waste.