Energy transfers

    OCR
    GCSE

    Energy is a conserved quantity that cannot be created or destroyed, only transferred between distinct stores via mechanical, electrical, heating, or radiation pathways. Analysis requires the quantitative evaluation of kinetic, gravitational potential, and elastic potential stores, alongside the calculation of work done and power as the rate of transfer. Candidates must assess system efficiency, accounting for the inevitable dissipation of energy to the thermal store of the surroundings, and evaluate methods to reduce unwanted energy transfers through thermal insulation.

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    Objectives
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    Exam Tips
    4
    Pitfalls
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    Key Terms
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    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for explicitly stating that energy is transferred from the gravitational potential store to the kinetic store as an object falls
    • Award 1 mark for correct substitution of values into the efficiency equation (Useful Output / Total Input) before converting to a percentage
    • Award 1 mark for explaining that lubrication reduces friction, thereby reducing the rate of energy transfer to the thermal store of the surroundings
    • Award 1 mark for linking a material's low thermal conductivity to a reduced rate of energy transfer by conduction
    • Credit responses that identify 'dissipated energy' as energy transferred to the thermal store of the surroundings, not 'lost' energy

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for explicitly stating that energy is transferred from the gravitational potential store to the kinetic store as an object falls
    • Award 1 mark for correct substitution of values into the efficiency equation (Useful Output / Total Input) before converting to a percentage
    • Award 1 mark for explaining that lubrication reduces friction, thereby reducing the rate of energy transfer to the thermal store of the surroundings
    • Award 1 mark for linking a material's low thermal conductivity to a reduced rate of energy transfer by conduction
    • Credit responses that identify 'dissipated energy' as energy transferred to the thermal store of the surroundings, not 'lost' energy

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When describing energy changes, always name the specific store (e.g., 'Chemical store') rather than just saying 'energy' to gain AO1 marks
    • 💡For 6-mark 'Level of Response' questions on insulation, structure your answer: Name the method → Describe the physics (e.g., trapped air) → Explain the reduction in transfer (e.g., prevents convection currents)
    • 💡Check your units immediately: if power is in kW, convert to W (x1000) before calculation unless the answer specifically asks for kWh
    • 💡In 'closed system' questions, explicitly state that 'total energy before equals total energy after' to secure the conservation of energy mark

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Describing energy as being 'created', 'destroyed', or 'used up' instead of being transferred or dissipated
    • Failing to convert time from minutes or hours into seconds when using the Power equation (P = E/t)
    • Confusing the mechanism of convection (fluid movement) with conduction (particle vibration) when explaining how cavity wall insulation works
    • Calculating efficiency as a value greater than 1 or 100% by dividing input by output instead of output by input

    Study Guide Available

    Comprehensive revision notes & examples

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    Key Terminology

    Essential terms to know

    Conservation of energy and system analysis
    Quantitative calculation of energy stores (Kinetic, GPE, Elastic)
    Power, efficiency, and dissipation
    Mechanisms of thermal transfer (Conduction, Convection, Radiation)

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    Explain
    Describe
    Suggest
    Compare

    Practical Links

    Related required practicals

    • •{"code":"PAG P2","title":"Investigation of the effectiveness of different materials as thermal insulators","relevance":"Directly assesses understanding of rate of cooling and material properties"}
    • •{"code":"PAG P1","title":"Determination of the Specific Heat Capacity of a material","relevance":"Links energy input (electrical work) to thermal store changes"}

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