AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Energy transfers in a system: Students should be able to describe, with examples, how in all system changes energy is dissipated, so that it is stored in less useful ways. This energy is often described as being ‘wasted’.
Dissipation occurs in every energy transfer because some energy spreads out into the surroundings, usually as thermal energy, making it less useful for further transfers.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Dissipation occurs in every energy transfer because some energy spreads out into the surroundings, usually as thermal energy, making it less useful for further transfers. For example, a moving car transfers energy from its kinetic store to thermal energy in the brakes, tyres and air; this thermal energy is dissipated and cannot easily be used to make the car move again. Similarly, a light bulb transfers electrical energy to light and thermal energy; the thermal energy is dissipated to the surroundings. This energy is often called 'wasted' because it is not transferred to the intended useful store.
What earns the marks
- States that in all system changes, some energy is dissipated to the surroundings, often as thermal energy.
- Describes a named example, such as a car braking or a light bulb, identifying the useful transfer and the dissipated transfer.
- Explains that dissipated energy is stored in less useful ways because it spreads out and is difficult to use for further useful transfers.
- Uses the term 'wasted' correctly to mean energy that is not transferred to the intended useful store.
- Recognises that dissipation occurs in every energy transfer, not just in inefficient devices.
Common mistakes and how to put them right
Saying energy is 'destroyed' or 'lost' when it is dissipated.
Put it right by stating energy is transferred to less useful stores, often thermal energy in the surroundings.
Assuming dissipation only happens in old or inefficient devices.
Put it right by explaining it happens in all system changes.
Confusing 'wasted' with energy that no longer exists.
Put it right by stating the energy still exists but is spread out and less useful.
Exam tips
- Name the useful energy transfer and the dissipated transfer in your example.
- Use the phrase 'stored in less useful ways' to match the specification wording.
- Explain why the dissipated energy is less useful, for example because it spreads out to the surroundings.
- Avoid saying energy is 'lost'; instead say it is dissipated or transferred to less useful stores.
Try the lesson
The start of the Energy transfers in a system: Students should be able to describe, with examples, how in all system changes energy is dissipated, so that it is stored in less useful ways. This energy is often described as being ‘wasted’. lesson, made from checked teaching notes for this specification point.
Have a go first
A ball is dropped and bounces a few times before stopping. Which statement describes what happens to the energy in this system change?
Key words
Say what each word means before you turn the card.
Dissipation of energy
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Wasted
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Thermal energy transfer
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Useful and wasted energy
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See every definition
- Dissipation of energy
- In all system changes, energy is transferred to the surroundings, often as thermal energy, so that it is stored in less useful ways.
- Wasted
- Energy that is not transferred to the intended useful store is often described as being this.
- Thermal energy transfer
- Energy spread out to the surroundings, for example in the brakes, tyres and air of a moving car, is dissipated in this form.
- Useful and wasted energy
- A system change involves a transfer to the intended useful store and a dissipated transfer that is not useful.
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