In 2024, renewable energy supplied 38% of Australia's electricity grid — up from just 15% a decade ago — yet coal still generates nearly half of all national power. You have travelled through ten lessons of energy, calculated efficiency, drawn Sankey diagrams, and explained why the Sydney Harbour Bridge grows 18 cm every summer. Now it is time to prove what you know in this checkpoint review before moving into the next block on energy sources and generation.
You have learned that no real device is 100% efficient and that energy transforms from one form to another without being created or destroyed.
An average Australian household uses about 15 kWh of electricity per day. A coal power station is 35% efficient, a solar panel is 20% efficient, and a wind turbine is 45% efficient.
Predict: Estimate how much total energy input (in kWh) each technology would need to supply that household's 15 kWh of useful electrical energy. Rank the three sources from least to most input energy required. Write your estimates and reasoning — you will check your predictions against the physics of efficiency at the end of the checkpoint.
Every concept from Lessons 1–10 connects. Hover over each node to see the link.
Score: 0 / 6
Quick Review
1. A coal power station is 35% efficient. For every 1,000 MJ of chemical energy in the coal, how much is wasted as thermal energy?
2. Which energy transformation occurs in a hydroelectric dam?
3. A student calculates the work done lifting a 30 kg box 2 metres as 60 J. What is wrong with this calculation?
4. On a hot day at Bondi Beach, the sand burns your feet but the water feels cool. The best explanation is:
5. A concrete bridge has no expansion joints. On a 45°C summer day, what is most likely to happen?
6. Draw a simple Sankey diagram for a device with 800 J input, 200 J useful output, and 600 J waste. Use a scale of 1 cm = 100 J. Label all arrows with energy values, forms, and units. Calculate and state the efficiency. 1 mark for correct arrow widths (8 cm, 2 cm, 6 cm). 1 mark for labels with values, forms and units. 1 mark for efficiency = 25%.
7. A family is choosing between two kettles. Kettle A is 2,000 W and boils 1 litre of water in 3 minutes. Kettle B is 1,000 W and boils the same amount in 6 minutes. Both are 90% efficient.
(a) Calculate the energy used by each kettle to boil the water.
(b) Explain which kettle is "better" — considering efficiency, energy use, time, and cost. Electricity costs $0.30 per kWh. 1 mark for calculating energy for Kettle A (360,000 J or 0.1 kWh). 1 mark for calculating energy for Kettle B (360,000 J or 0.1 kWh). 1 mark for explaining that both use the same energy but Kettle A is faster. 1 mark for cost calculation and recommendation with reasoning.
8. The Nullarbor Plain in South Australia has summer temperatures of 50°C and winter temperatures of 5°C. A new railway is being built across the plain. Engineers must decide between jointed track (with gaps) and continuously welded rail (no gaps).
Using your knowledge of thermal expansion, conduction, specific heat capacity, and energy transfer, evaluate both options for this environment. Consider: temperature range, material expansion, passenger comfort, maintenance, and safety. Recommend one design and justify your choice using physics principles. 1 mark for calculating or describing the temperature range (45°C) and its effect on steel expansion. 1 mark for explaining how jointed track works (gaps allow expansion, prevent buckling). 1 mark for explaining how welded rail works (constrained expansion, requires resistance to buckling). 1 mark for evaluating specific Nullarbor challenges (extreme heat, remote location, maintenance access). 1 mark for justified recommendation with physics reasoning.
1. B — Useful = 1,000 × 0.35 = 350 MJ. Waste = 1,000 − 350 = 650 MJ.
2. C — Water at height has GPE → falls and gains KE → spins turbines → generates electrical energy.
3. A — Force = 30 × 10 = 300 N. Work = 300 × 2 = 600 J. The student used mass instead of force.
4. D — Sand c ≈ 800 J/kg°C, water c = 4,200 J/kg°C. Same energy input: sand heats ~5× more.
5. B — Concrete expands when heated. Without gaps, compressive stress causes buckling.
Q6 (3 marks): Input arrow: 8 cm wide, labelled "800 J chemical energy" [0.5]. Useful output: 2 cm wide, labelled "200 J useful energy" [0.5]. Waste: 6 cm wide, labelled "600 J waste thermal energy" [0.5]. Scale stated: 1 cm = 100 J [0.5]. Efficiency = (200 ÷ 800) × 100 = 25% [1 mark].
Q7 (4 marks): (a) Kettle A: 2,000 W × 180 s = 360,000 J (0.1 kWh) [0.5]. Kettle B: 1,000 W × 360 s = 360,000 J (0.1 kWh) [0.5]. (b) Both use the same energy because they heat the same water [0.5]. Kettle A is more powerful, doing the same work in half the time [0.5]. Cost: both = 0.1 × $0.30 = $0.03 per boil [0.5]. Recommendation: Kettle A for busy households where speed matters; Kettle B for energy-conscious users on a budget (lower upfront cost) [0.5].
Q8 (5 marks): Temperature range = 50 − 5 = 45°C [0.5]. Steel rails expand by approximately 5.4 mm per 10 m per 45°C [0.5]. Jointed track: Gaps allow free expansion, eliminating buckling risk [0.5]. Disadvantages: noise, vibration, higher maintenance, speed restrictions [0.5]. Welded rail: Smoother ride, lower long-term maintenance, higher speeds [0.5]. Disadvantages: requires massive concrete sleepers to resist buckling; extreme heat (50°C) creates enormous compressive forces [0.5]. Nullarbor challenges: Remote location makes maintenance difficult; extreme heat increases buckling risk; 45°C range is among the highest in Australia [0.5]. Recommendation: Jointed track for the Nullarbor [0.5]. Justification: the extreme temperature range and remote location make maintenance-critical. Jointed track fails safely (gaps widen) and is easier to repair in isolated areas. Welded rail would require constant monitoring and speed restrictions on extreme heat days, which is impractical 500 km from the nearest town [0.5].
Want to review any section before moving on?
Tick when you can explain energy conservation, calculate efficiency, identify heat transfer methods, and apply thermal concepts to real problems.