Year 9 Science · Unit 3 · Lesson 1
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Learning Goals
1. Explain the difference between an energy transfer and an energy transformation.
Real-world context: from coal to a cool breeze
Many Australian homes get some of their electricity from coal-fired power stations. That electricity runs everyday devices, such as an electric fan on a hot summer afternoon.
2. The table shows the coal-to-fan chain in order. For each stage, write the form of energy at the end of the stage, and whether the stage is a transfer or a transformation.
| Stage | Energy form at the end of this stage | Transfer or transformation? |
|---|---|---|
| 1. Coal is burned in a boiler | ||
| 2. The heat from the fire boils water into steam | ||
| 3. The steam pushes on turbine blades and spins them | ||
| 4. The spinning turbine turns a generator | ||
| 5. Electricity flows along wires to your home | ||
| 6. The fan’s motor spins the fan blades |
3. At every stage, some energy becomes heat that spreads into the surroundings. Is this heat energy “lost”? Explain your answer using the law of conservation of energy.
Data: following 1,000 MJ of coal energy to the fan
Table 1 follows 1,000 MJ of chemical energy in coal along the chain above. It shows how much of that energy is still in the form we want at the end of three stages.
| End of stage | Energy in the wanted form (MJ) | Energy that became waste heat at this stage (MJ) |
|---|---|---|
| Start: chemical energy in the coal | 1,000 | – |
| Electrical energy leaving the power station | 330 | |
| Electrical energy arriving at homes | 310 | |
| Kinetic energy of the fan blades | 279 |
Source: typical values from Lesson 1 (a coal-fired power station is about 33% efficient; an electric motor turns about 90% of its electrical energy into motion). The loss in the power lines is an example value.
4. Complete the last column of Table 1. At which stage is the biggest amount of energy lost as heat?
Stage that wastes the most
5. What percentage of the coal’s chemical energy ends up as kinetic energy of the fan blades?
Percentage %
6. A student looks at Table 1 and says: “Only 279 MJ is left at the end, so 721 MJ of energy has been destroyed.” Use the table to explain what is wrong with this statement.
7. A cyclist rides home at night. A small dynamo, turned by the front wheel, powers the bike’s headlight. Trace the energy from the cyclist’s breakfast to the light shining on the road. Name the form of energy at each step, label each step as a transfer or a transformation, and say where energy is wasted along the way.