Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Explain that where there are energy transfers in a closed system there is…
Full specification wording
Topic 8 – Energy – forces doing work: 8.3 Explain that where there are energy transfers in a closed system there is no net change to the total energy in that system
A closed system is one in which no energy enters or leaves from outside, so energy can only move between stores inside it.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 3 of 15
Study notes
From the checked teaching notes for this specification point.
The idea
A closed system is one in which no energy enters or leaves from outside, so energy can only move between stores inside it. When a falling ball transfers energy from its gravitational potential store to its kinetic store, the total of all the stores stays the same: the loss from one store equals the gain in another. Energy may also be transferred by heating to the surroundings, but in a truly closed system those surroundings are part of the system, so the total is still unchanged. The key idea is conservation: energy is neither created nor destroyed, only transferred. A correct answer therefore states that the total energy stays constant even though individual stores change.
What earns the marks
- States that the total energy of a closed system stays constant when energy is transferred between stores.
- Identifies that a decrease in one energy store is matched by an equal increase in another store within the system.
- Explains that no energy enters or leaves a closed system from outside, so the net change is zero.
- Recognises that energy may be transferred by heating or by work between parts of the system without altering the total.
Common mistakes and how to put them right
Claims that energy is used up or destroyed during a transfer.
Put it right by stating that energy is conserved and only moves between stores.
Assumes the total energy falls because one store decreases.
Put it right by noting that another store rises by the same amount.
Treats an open system as closed and ignores energy leaving to the surroundings.
Put it right by checking whether energy crosses the system boundary.
Exam tips
- Read the question for the words 'closed system' before choosing an answer about total energy.
- Check each option for the idea of conservation rather than a change in total energy.
- Eliminate options that say energy is lost or created, because these contradict conservation.
Try the lesson
The start of the Topic 8 – Energy – forces doing work: 8.3 Explain that where there are energy transfers in a closed system there is no net change to the total energy in that system lesson, made from checked teaching notes for this specification point.
Have a go first
A ball is dropped inside a sealed, insulated box. As it falls, energy is transferred from its gravitational store to its kinetic store. What happens to the total energy of the closed system during the fall?
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