Year 9 Science · Unit 3 · Lesson 24
Challenge Worksheet
Learning Goals
1. Complete the table from memory. For each system, give its energy transformation chain. Then say how much CO₂ it releases and when, and whether its supply is baseload, intermittent or dispatchable.
| System | Energy transformation chain | CO₂ emissions, and reliability |
|---|---|---|
| Coal power station | ||
| Solar farm with a battery | ||
| Pumped hydro | ||
| Green hydrogen plant |
Investigation: testing a sous-vide cooker
A sous-vide cooker is a heater and pump that clips onto a pot of water. A class put one rated at 800 W into 4.0 kg of water in a pot with no lid, and recorded the temperature every 5 minutes.
| Time (min) | Temperature (°C) |
|---|---|
| 0 | 20.0 |
| 5 | 33.5 |
| 10 | 47.0 |
| 15 | 60.5 |
| 20 | 74.0 |
Source: sample class results.
2. (a) Use E = P × t to find the electrical energy supplied in 20 minutes. (b) Use Q = m × c × ΔT, with c = 4,200 J/kg·°C for water, to find the energy the water gained. (c) Find the cooker’s efficiency, to one decimal place.
(a) Supplied J
(b) Gained J
(c) Efficiency %
3. (a) How much energy was wasted, and where did it go? (b) What does the pattern in Table 1 tell you about the rate of heating? (c) Suggest two changes that would waste less energy, and name the heat transfer each one reduces.
(a) Wasted J
Find the errors: a student’s essay on Australia’s energy future
A student began an essay with “Australia is at a turning point in its energy history”, then wrote these seven sentences.
| # | Sentence from the essay |
|---|---|
| 1 | Heat moves through liquids and gases by conduction, which is why convection currents form in the atmosphere and drive our weather. |
| 2 | In homes, appliances are connected in series so that each one receives the same voltage. |
| 3 | The National Electricity Market (NEM) links the grids of Queensland, New South Wales, the ACT, Victoria, South Australia and Tasmania, while Western Australia and the Northern Territory run their own separate grids. |
| 4 | Unlike fossil fuels, hydrogen is a primary energy source that can be collected straight from the environment. |
| 5 | Transformers step up the voltage before electricity is sent along transmission lines, so the current is smaller and less energy is lost as heat. |
| 6 | Australia’s CO₂ emissions per person are below the world average, which shows we have already done enough. |
| 7 | Finally, a well-designed power station can turn all of the energy in its fuel into electricity, because energy is conserved. |
4. Five of the seven sentences contain a scientific error. For each of the five, write the sentence number and a correct version of the sentence.
| # | Correct version of the sentence |
|---|---|
5. What is the most important energy challenge facing Australia in the next 20 years? Argue your case using at least three ideas from different parts of the Energy unit.