Energy Transfer

    OCR
    GCSE

    Energy is governed by the fundamental principle of conservation: it cannot be created or destroyed, only transferred between distinct stores within a closed system. Candidates must quantify these transfers using specific formulae for kinetic, gravitational potential, and elastic potential energy, while analyzing the rate of transfer as power. The concept of efficiency is critical, requiring an understanding of useful versus dissipated energy, particularly in the context of thermal degradation to the surroundings and methods to reduce unwanted energy transfer.

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    Objectives
    3
    Exam Tips
    4
    Pitfalls
    4
    Key Terms
    5
    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 (mechanically, electrically, by heating, or by radiation)
    • Credit responses that define Power as the rate of energy transfer or work done (1 watt = 1 joule per second)
    • Award 1 mark for correct substitution of values into the efficiency equation, ensuring useful energy output is the numerator
    • Credit the explanation that lubrication reduces friction, thereby reducing the energy transferred to the thermal store of the surroundings
    • For thermal conductivity, award marks for linking higher thermal conductivity to a higher rate of energy transfer by conduction across a material

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly calculated the energy, but check your units — did you convert minutes to seconds?"
    • "Avoid saying 'heat is lost'. Instead, state that 'energy is dissipated to the thermal store of the surroundings'."
    • "Good identification of the energy stores. To improve, explicitly name the pathway (e.g., 'mechanically') that transfers the energy."
    • "Your rearrangement of the equation was incorrect. Practice isolating the variable before substituting the numbers."

    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 (mechanically, electrically, by heating, or by radiation)
    • Credit responses that define Power as the rate of energy transfer or work done (1 watt = 1 joule per second)
    • Award 1 mark for correct substitution of values into the efficiency equation, ensuring useful energy output is the numerator
    • Credit the explanation that lubrication reduces friction, thereby reducing the energy transferred to the thermal store of the surroundings
    • For thermal conductivity, award marks for linking higher thermal conductivity to a higher rate of energy transfer by conduction across a material

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When describing energy transfers in a closed system, explicitly state that 'total energy remains constant' to satisfy the Law of Conservation of Energy
    • 💡In calculations involving Specific Heat Capacity, always check if the mass is given in grams and convert to kilograms before substitution
    • 💡For 6-mark Level of Response questions on insulation, structure your answer to cover: control variables, the independent variable (e.g., thickness), and the dependent variable (temperature drop over time)

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Stating that 'energy is lost' or 'used up' rather than 'dissipated to the thermal store of the surroundings'
    • Failing to convert time from minutes into seconds when using the Power equation (P = E/t), leading to incorrect magnitude
    • Confusing 'thermal conductivity' (rate of transfer) with 'specific heat capacity' (energy to raise temperature)
    • Calculating efficiency as a value greater than 1 (or >100%) by dividing total input by useful output

    Study Guide Available

    Comprehensive revision notes & examples

    Read Study Guide

    Key Terminology

    Essential terms to know

    Conservation of energy and closed systems
    Quantitative analysis of energy stores (Kinetic, GPE, Elastic)
    Power, efficiency, and dissipation
    Thermal conductivity and insulation methods

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    Explain
    Describe
    Suggest
    Evaluate

    Practical Links

    Related required practicals

    • •{"code":"PAG P2","title":"Investigation of Specific Heat Capacity","relevance":"Measuring energy input and temperature change to calculate c"}
    • •{"code":"PAG P2","title":"Thermal Insulation","relevance":"Investigating effectiveness of different materials as thermal insulators"}

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