Changes in energy

    AQA
    GCSE

    Energy is conserved within a closed system; it cannot be created or destroyed, only transferred between different stores, dissipated, or stored in less useful ways. Candidates must quantify these changes using specific formulae for kinetic energy, gravitational potential energy, and elastic potential energy, while applying the principle of conservation of energy to dynamic systems. Analysis of energy transfer rates defines power, while the ratio of useful output to total input determines efficiency, necessitating calculations involving specific heat capacity to understand thermal energy changes.

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    Objectives
    3
    Exam Tips
    3
    Pitfalls
    5
    Key Terms
    4
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for correct substitution of values into the equation Ek = 0.5mv^2 prior to any rearrangement
    • Credit responses that explicitly identify the 'thermal store of the surroundings' as the destination for dissipated energy
    • Award 1 mark for stating that the total energy in a closed system remains constant
    • Candidates must link a reduction in unwanted energy transfers to specific methods of thermal insulation, such as lubrication or cavity wall insulation

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for correct substitution of values into the equation Ek = 0.5mv^2 prior to any rearrangement
    • Credit responses that explicitly identify the 'thermal store of the surroundings' as the destination for dissipated energy
    • Award 1 mark for stating that the total energy in a closed system remains constant
    • Candidates must link a reduction in unwanted energy transfers to specific methods of thermal insulation, such as lubrication or cavity wall insulation

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Always write down the equation, then substitute the numbers, and finally rearrange; this method secures method marks even if the final calculation is incorrect
    • 💡When describing energy changes, use the 'Store A to Store B' structure; avoid vague terms like 'energy is used up'
    • 💡Check efficiency calculations carefully; if the result is greater than 1 (or 100%), the numerator and denominator are inverted

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Neglecting to square the velocity term (v^2) in kinetic energy calculations, leading to significant numerical errors
    • Failing to convert units to SI standards before calculation, specifically leaving mass in grams or time in minutes
    • Describing energy as being 'created' or 'destroyed' rather than transferred, violating the conservation of energy principle

    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    Describe
    Explain
    Compare
    Suggest
    Determine

    Practical Links

    Related required practicals

    • •{"code":"Required Practical 1","title":"Specific Heat Capacity","relevance":"Determining the specific heat capacity of a material by linking energy input to temperature change"}
    • •{"code":"Required Practical 2","title":"Thermal Insulation","relevance":"Investigating the effectiveness of different materials as thermal insulators"}

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