⚡ Energy Efficiency and Sankey Diagrams

What you’ll learn

1. Nothing Vanishes — It Just EscapesExplain the conservation of energy and why 'wasted' energy is never destroyed but escapes as heat.Energy can only be transferred or change form, never be created or destroyed. When a machine 'wastes' energy it sends it somewhere useless — almost always heat. An old filament bulb turns only about 2% of its electricity into light and the rest into heat, so it is really a heater that glows.
2. Efficiency Is Just a FractionCalculate efficiency as useful energy out divided by total energy in, and explain why it cannot exceed 100%.Efficiency = (useful energy out ÷ total energy in) × 100%. It is a score out of 100 for how much of your energy did the job. Because useful plus wasted equals the total input, efficiency can never top 100%. Everyday machines range from ~2% (filament bulb) to ~90% (electric motor).
3. The Sankey Diagram: A Picture of the FlowRead and interpret a Sankey diagram, using arrow width for energy amount and the balancing rule for conservation.A Sankey diagram draws energy as arrows whose width equals the amount of energy. The input splits into useful and wasted branches, and because energy is conserved the branches out must add up to the arrow in. A wide useful branch means an efficient machine.
4. Where Does the Wasted Energy Go?Explain that wasted energy becomes heat via friction and electrical resistance, using a car engine as the example.Friction between moving parts and electrical resistance in wires both generate heat, which is why wasted energy nearly always ends up as heat that spreads out and can't be recovered. A petrol engine turns only about 20–40% of fuel energy into movement; the rest leaves as exhaust heat, cooling losses and friction.
5. Work: Force × DistanceDefine work as force × distance, measured in joules, and relate it to energy transferred.Work is done when a force moves something a distance: work = force × distance, in joules (newton-metres). It is the same joule as energy, because doing work transfers energy. With a fixed force, work grows in a straight line with distance, and no movement means no work.
6. Putting It Together: A Real MachineCombine work and efficiency to evaluate a real lifting machine end to end.For a lifting machine, useful output is the work done on the load (force × distance). Comparing that to the energy supplied gives efficiency, and the difference is wasted heat. A winch lifting 200 N through 3 m (600 J of work) on 750 J of electricity is 80% efficient, wasting 150 J.
7. Why the Wasted Joules MatterConnect efficiency to real energy use and cost, and apply an analytical habit to everyday machines.Wasted joules are paid-for energy turned into useless heat. Swapping filament bulbs for LEDs saves large amounts of electricity for the same light, and an inefficient device can cost energy twice in summer by adding heat a cooler must remove. Improving efficiency always means cutting friction and resistance losses.

Questions this course answers

Grounded in trusted sources

• Luminous efficacy — incandescent bulbs 0.7–2.6% of energy to visible light; LEDs 11–32%: https://en.wikipedia.org/wiki/Luminous_efficacy
• Engine efficiency — typical petrol/gasoline engines convert about 20–40% of fuel energy to useful work: https://en.wikipedia.org/wiki/Engine_efficiency
• Electric motor — brushless DC motors typically 85%+ efficient, up to 96.5%: https://en.wikipedia.org/wiki/Electric_motor
• Electric kettle measured efficiency ~84% heating water: https://www.cambridgeclarion.org/85.html
• Conservation of energy: https://en.wikipedia.org/wiki/Conservation_of_energy
• Work (physics) — work = force × distance, measured in joules: https://en.wikipedia.org/wiki/Work_(physics)
• Sankey diagram — energy-flow diagram with arrow width proportional to quantity: https://en.wikipedia.org/wiki/Sankey_diagram

Every Wunder lesson is built from real, reputable sources — never invented.

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