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Conservation and dissipation of energy
Conservation and dissipation of energy turns the energy-store model into real-world explanations. Students describe closed systems, useful and wasted transfers, efficiency, and how insulation reduces unwanted energy transfer. The topic also separates closely related ideas: thermal conductivity is a material property, wall thickness is a distance effect, and dissipation means energy spreads into less useful stores rather than being destroyed. Strong answers name both the store and the transfer pathway.
23
Objectives
115
Flashcards
115
Questions
90 min
Study time
AQAGCSEPhysicsEnergy
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Syllabus checklist
What you need to know
23 objective pages available
Energy transfers in a system13 objectives
- State that energy can be transferred usefully, stored or dissipated but cannot be created or destroyed.
- Describe examples of energy transfers in a closed system with no net change to total energy.
- Explain that energy is often dissipated into less useful stores during system changes.
- Use the term wasted energy to describe energy transferred in less useful ways.
- Explain how lubrication reduces unwanted energy transfers by reducing friction.
- Explain how thermal insulation reduces unwanted energy transfers by heating.
- Describe how thermal conductivity affects the rate of energy transfer by conduction.
- Describe how wall thickness affects the rate of cooling of a building.
- Describe how thermal conductivity of wall materials affects the rate of cooling of a building.
- Required practical activity 2 (physics only): investigate the effectiveness of different materials as thermal insulators.
- Required practical activity 2 (physics only): investigate factors that may affect thermal insulation properties.
- Identify apparatus and techniques used in thermal insulation practical work.
- Interpret data from thermal conductivity or insulation investigations.
Efficiency10 objectives
- Calculate efficiency using useful energy output divided by total energy input.
- Calculate efficiency using useful power output divided by total power input.
- Recall and apply both efficiency equations.
- Express efficiency as a decimal.
- Express efficiency as a percentage.
- Convert efficiency values between decimals and percentages.
- Explain why no real energy transfer is perfectly efficient.
- Identify useful and wasted energy transfers in a device or process.
- (HT only) Describe ways to increase the efficiency of an intended energy transfer.
- (HT only) Explain how reducing unwanted energy transfers improves efficiency.
Key terms
Energy transferEnergy conservationclosed systemenergy transferdissipated energyless useful storewasted energyuseful energylubricationfrictionthermal insulationunwanted energy transfers
Exam tips
- Understand Energy Conservation: Explain Energy transfers in a system clearly: energy cannot be created or destroyed; it can only be transferred or transformed.
- Understand Closed Systems: Familiarize yourself with examples of energy transfers in closed systems, ensuring you can explain how energy remains constant despite changes.
Common mistakes
- Misunderstanding Energy Conservation: Remember that energy cannot be created or destroyed; it can only be transferred, stored, or dissipated.
- Misunderstanding Closed Systems: Emphasize that in a closed system, energy is conserved and can only be transferred or transformed, not created or destroyed.
Practice preview
- A machine uses 500 J of energy input and produces 400 J of useful energy output. What is the efficiency of the machine?
- If a device has an efficiency of 90% and uses 2000 J of energy, how much useful energy does it produce?
- A light bulb has an efficiency of 75% and consumes 60 W of power. What is the useful power output of the light bulb?
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