Nuclear Fusion

    OCR
    GCSE

    Nuclear fusion is the process by which two light atomic nuclei combine to form a single, heavier nucleus, resulting in a significant release of energy. This process constitutes the primary energy source for stars, where extreme temperatures and pressures are necessary to overcome the electrostatic repulsion between positively charged nuclei. The energy released originates from a mass defect, where the mass of the product nucleus is less than the sum of the reactant nuclei, governed by the mass-energy equivalence principle. Unlike nuclear fission, fusion does not produce long-lived radioactive waste products, though achieving sustainable controlled fusion on Earth remains a complex engineering challenge.

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    Objectives
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    Exam Tips
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    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 stating that nuclear fusion involves two light nuclei joining to form a heavier nucleus
    • Award 1 mark for identifying that the mass of the products is slightly less than the mass of the reactants
    • Award 1 mark for stating that the lost mass is converted into energy (or referencing E=mc² qualitatively)
    • Award 1 mark for explaining that high temperatures are required to increase kinetic energy and overcome electrostatic repulsion
    • Credit responses that identify fusion as the energy source for stars

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly defined fusion, but ensure you specify 'nuclei' instead of 'atoms' to secure the mark"
    • "Good recall of the process. To access higher marks, explain *why* high temperatures are necessary in terms of forces"
    • "You confused fission and fusion here—remember 'fusion' sounds like 'fuse' (join together)"
    • "Excellent link to mass conversion. To improve, explicitly state that the mass of the products is less than the reactants"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that nuclear fusion involves two light nuclei joining to form a heavier nucleus
    • Award 1 mark for identifying that the mass of the products is slightly less than the mass of the reactants
    • Award 1 mark for stating that the lost mass is converted into energy (or referencing E=mc² qualitatively)
    • Award 1 mark for explaining that high temperatures are required to increase kinetic energy and overcome electrostatic repulsion
    • Credit responses that identify fusion as the energy source for stars

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Always use the term 'nuclei' instead of 'atoms' when describing the fusion process; examiners penalize loose terminology here
    • 💡For Higher Tier questions on conditions, do not just say 'high heat is needed'—you must explain that high kinetic energy is required to overcome electrostatic repulsion
    • 💡In 6-mark comparison questions, use a table to contrast fission and fusion across categories: process definition, nuclei size, and energy yield

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Referring to 'atoms' fusing rather than 'nuclei', which is a critical terminology error in nuclear physics
    • Confusing the definitions of fission (splitting) and fusion (joining), often swapping the descriptors
    • Stating that mass is simply 'lost' or 'disappears' without explaining it is converted into energy
    • Failing to link high temperature explicitly to the need to overcome the electrostatic repulsion between positively charged nuclei

    Study Guide Available

    Comprehensive revision notes & examples

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    Key Terminology

    Essential terms to know

    Formation of heavy nuclei from light nuclei
    Electrostatic repulsion and high temperature requirements
    Mass-energy equivalence and mass defect
    Stellar energy generation
    Isotopes of hydrogen (Deuterium and Tritium)

    Likely Command Words

    How questions on this topic are typically asked

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