Energy stores and systems

    AQA
    GCSE

    Energy is a conserved scalar quantity defined by the capacity to do work, existing in specific stores such as kinetic, gravitational potential, and thermal. Analysis of physical systems requires tracking the redistribution of energy between these stores via mechanical, electrical, heating, or radiation pathways. Candidates must apply the Principle of Conservation of Energy to closed systems, equating total energy before and after events, while accounting for dissipation into the surroundings in open systems. Quantitative assessment involves calculating specific store values using standard formulae and determining the rate of transfer (power) and the efficiency of the process.

    0
    Objectives
    3
    Exam Tips
    3
    Pitfalls
    4
    Key Terms
    4
    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 [initial] store to the [final] store via a specific pathway (mechanical, electrical, heating, or radiation).
    • Credit responses that correctly substitute values into the equations for Kinetic Energy (Ek = 0.5mv²), Gravitational Potential Energy (Ep = mgh), or Elastic Potential Energy (Ee = 0.5ke²) before attempting rearrangement.
    • Award 1 mark for identifying that in a closed system, the total energy remains constant, equating energy lost from one store to energy gained by another.
    • Candidates must link 'wasted' energy specifically to the dissipation of energy to the thermal store of the surroundings, causing a temperature rise.

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for explicitly stating that energy is transferred from the [initial] store to the [final] store via a specific pathway (mechanical, electrical, heating, or radiation).
    • Credit responses that correctly substitute values into the equations for Kinetic Energy (Ek = 0.5mv²), Gravitational Potential Energy (Ep = mgh), or Elastic Potential Energy (Ee = 0.5ke²) before attempting rearrangement.
    • Award 1 mark for identifying that in a closed system, the total energy remains constant, equating energy lost from one store to energy gained by another.
    • Candidates must link 'wasted' energy specifically to the dissipation of energy to the thermal store of the surroundings, causing a temperature rise.

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When calculating velocity from kinetic energy, write down the rearranged formula first, then substitute, and do not forget the square root step at the end.
    • 💡For 6-mark 'Describe the energy changes' questions, structure your answer chronologically: Initial Store → Transfer Pathway → Final Store + Dissipation.
    • 💡Memorise the Specific Heat Capacity equation (ΔE = mcΔθ) and the Power equations (P = E/t and P = W/t), as these are frequently tested in multi-step calculations.

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Confusing energy 'stores' with energy 'transfers' (e.g., incorrectly referring to 'electrical energy' or 'light energy' as stores rather than transfer pathways).
    • Failing to square the velocity (v²) in kinetic energy calculations or extension (e²) in elastic potential energy calculations, leading to significant arithmetic errors.
    • Neglecting to convert units to SI standards before calculation, particularly mass from grams to kilograms or extension from centimetres to metres.

    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    Describe
    Explain
    Compare
    Suggest

    Practical Links

    Related required practicals

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

    Ready to test yourself?

    Practice questions tailored to this topic