Energy Conservation
Year 10 (IGCSE) 🌡️ Energy & Thermodynamics Apply the principle of energy conservation; draw Sankey diagrams.
♻️ The Law of Conservation of Energy
Energy is never created or destroyed. In any process, the total amount of energy stays constant — it just changes form or moves from place to place.
♻️ Conservation of Energy
$$E_{\text{input}} = E_{\text{useful output}} + E_{\text{wasted}}$$🏋️ Person lifting a box: Chemical energy (muscles) → gravitational PE (box) + thermal energy (body heat from inefficiency)
🔌 Electric motor: Electrical energy → kinetic energy (shaft) + thermal energy (friction/resistance losses)
Wasted energy is usually dissipated as thermal energy into the surroundings — it becomes so spread out it can't be recovered for useful work.
📊 Sankey Diagrams
A Sankey diagram shows the flow of energy through a system. Arrow width represents the amount of energy.
💡 LED bulb (10 W input):
→ Useful: 9 W light output (wide right arrow)
→ Wasted: 1 W heat (thin downward arrow)
Efficiency = 9/10 × 100% = 90% 🏆
→ Useful: 9 W light output (wide right arrow)
→ Wasted: 1 W heat (thin downward arrow)
Efficiency = 9/10 × 100% = 90% 🏆
🚗 Petrol car engine:
Input: 100 J chemical energy in petrol
→ Useful: 25 J kinetic energy
→ Wasted: 75 J heat (exhaust + engine friction)
Efficiency = 25% 😢 Most energy is wasted!
Input: 100 J chemical energy in petrol
→ Useful: 25 J kinetic energy
→ Wasted: 75 J heat (exhaust + engine friction)
Efficiency = 25% 😢 Most energy is wasted!
Key Sankey diagram rule: The total width of all output arrows must equal the input arrow width!
💡 Improving Efficiency
Engineers work to reduce energy waste in devices and buildings.
| ⚙️ Device/System | 🔧 How efficiency is improved |
|---|---|
| Car engines | Better lubricants reduce friction; hybrid systems recover braking energy |
| Home heating | Loft insulation, double glazing, draught excluders reduce heat loss |
| Lighting | LED bulbs (90% efficient) replace filament bulbs (5% efficient) |
| Power stations | Combined heat and power (CHP) systems use waste heat too |
| Electric motors | Superconducting magnets reduce resistance losses |
Ready to test yourself? Click the Quiz tab above to answer questions on this topic!
♻️ Energy Efficiency Calculator
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