Reducing Unwanted Energy Transfers
Get to grips with Reducing Unwanted Energy Transfers for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Unwanted energy transfers can be reduced by lubrication and by insulation, using thicker walls and materials with low thermal conductivity.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Unwanted energy transfers can be reduced by lubrication, thermal insulation and streamlining, and each works by tackling a specific cause of dissipation.
Friction between moving parts causes energy to be dissipated to thermal energy stores. Lubricating the parts with oil reduces the friction, so less energy is dissipated and more is transferred usefully.
In buildings, the rate of energy transfer through the walls depends on the thickness of the walls and their thermal conductivity. Thicker walls and materials with lower thermal conductivity both reduce the rate of transfer, so the building cools more slowly.
Revision notes
Reducing friction
Friction between moving parts dissipates energy to thermal energy stores.
Lubricating with oil or grease reduces the friction, so less energy is dissipated and a greater proportion is transferred usefully. This increases the efficiency of the machine.
Thermal insulation in buildings
The rate of energy transfer through a wall depends on its thickness and its thermal conductivity.
Thicker walls transfer energy more slowly. Materials with lower thermal conductivity also transfer energy more slowly. Both keep the building warmer for longer.
Other methods
Streamlining reduces air resistance, so less energy is dissipated as an object moves through air.
Double glazing traps a layer of air or gas between panes, and because gases have low thermal conductivity this reduces the rate of energy transfer through windows.
Key points
- Lubrication reduces friction between moving parts.
- Less friction means less energy dissipated.
- Thicker walls reduce the rate of energy transfer.
- Lower thermal conductivity reduces the rate of transfer.
- Streamlining reduces air resistance.
- Double glazing traps a low conductivity gas layer.
Worked examples
Example 1
Explain how thermal insulation reduces the rate of energy transfer from a house. [2 marks]
Model answer
Insulation has a low thermal conductivity (1 mark), so energy is transferred through it more slowly and the house cools down less quickly (1 mark).
Example 2
State two factors that affect the rate of energy transfer through the walls of a building. [2 marks]
Model answer
The thickness of the walls (1 mark) and the thermal conductivity of the material they are made from (1 mark).
Example 3
Explain how double glazing reduces energy transfer through a window. [2 marks]
Model answer
Double glazing traps a layer of air or gas between the two panes of glass (1 mark), and because gases have a low thermal conductivity this slows the rate of energy transfer (1 mark).
Common mistakes
Saying insulation stops energy transfer.
It reduces the RATE of transfer; it does not stop it.
Forgetting wall thickness.
Both thickness and thermal conductivity affect the rate.
Saying lubrication removes friction.
It reduces friction rather than eliminating it.
Not explaining why a gas layer helps.
Gases have low thermal conductivity, which is the reason.
Exam tips
- Say rate of energy transfer, not just energy transfer.
- Give both thickness and conductivity as factors.
- Link each method to the transfer it reduces.
- Use the term thermal conductivity precisely.
Key terms
- Thermal conductivity
- How readily a material transfers energy by heating.
- Insulation
- A material reducing the rate of thermal energy transfer.
- Lubrication
- Reducing friction between moving surfaces.
- Streamlining
- Shaping an object to reduce air resistance.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.