Year 9 Science · Unit 3 · Lesson 4
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Learning Goals
Compare two
Use the Sankey data below to compare a petrol car engine (25% efficient) and an electric motor in an EV (85% efficient). Both receive 100 J of input energy. Complete the comparison table.
Petrol engine: 100 J input → 25 J kinetic energy (useful) + 45 J exhaust heat + 20 J engine heat + 10 J sound/friction (waste)
Electric motor: 100 J input → 85 J kinetic energy (useful) + 10 J heat from resistance + 5 J sound (waste)
| Feature | Petrol car engine | Electric motor (EV) |
|---|---|---|
| Total energy input (J) | ||
| Useful energy output (J) | ||
| Total waste energy (J) | ||
| Main form(s) of waste | ||
| Efficiency (%) |
(a) If both engines run for a long trip using 10,000 J of input energy each, how many more joules of useful kinetic energy does the EV produce compared to the petrol engine?
(b) On a Sankey diagram, which engine would have a narrower waste arrow? Explain what this tells you visually.
Because… chain
Complete each right-hand box to show the consequence that results. The chain starts with reducing the waste heat arrow in a Sankey diagram and ends at an environmental benefit.
Environmental benefit:
1. A student draws a Sankey diagram for an incandescent bulb where the "light" arrow is the widest arrow on the diagram. Identify the error and explain how the diagram should look, using the lesson's content on efficiency.
2. The Australian Energy Council reports that replacing household incandescent bulbs with LEDs could reduce lighting energy use by over 70% nationwide. Using Sankey diagram reasoning, explain why this saving is possible even though both devices produce light.
Wrap Up
In one sentence, what was the main idea of this lesson?