Domestic uses and safety

    AQA
    GCSE

    Domestic electricity supplies in the UK are delivered as alternating current (AC) at a frequency of 50 Hz and a potential difference of approximately 230 V, distinct from direct current (DC) sources like batteries. Safety within the domestic environment relies on the precise configuration of the three-pin plug, utilizing live (brown), neutral (blue), and earth (green/yellow) wires to manage potential difference and provide a low-resistance path to ground during faults. Protective mechanisms, including fuses and circuit breakers, must be understood in terms of their thermal or magnetic responses to current surges that exceed rated values. Candidates must also quantify electrical performance by calculating power ratings and energy transfer, linking these concepts to appliance efficiency and domestic energy costs.

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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 alternating current (ac) continuously changes direction, whereas direct current (dc) flows in one direction only
    • Award 1 mark for identifying the live wire (brown) as carrying the alternating potential difference from the supply
    • Credit responses that explain the earth wire provides a low resistance path to ground, causing a surge in current that melts the fuse
    • Award 1 mark for linking high potential difference in the National Grid to reduced current and consequently reduced thermal energy dissipation (P=I²R)

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that alternating current (ac) continuously changes direction, whereas direct current (dc) flows in one direction only
    • Award 1 mark for identifying the live wire (brown) as carrying the alternating potential difference from the supply
    • Credit responses that explain the earth wire provides a low resistance path to ground, causing a surge in current that melts the fuse
    • Award 1 mark for linking high potential difference in the National Grid to reduced current and consequently reduced thermal energy dissipation (P=I²R)

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When explaining electric shocks, explicitly state that the person provides a conducting path between the live wire (230V) and earth (0V)
    • 💡Memorize the specific potential differences: Live-Neutral (230V) and Live-Earth (230V); do not assume the neutral wire has 'no voltage' relative to the live wire
    • 💡For 6-mark safety questions, structure your answer chronologically: Fault occurs → Live touches case → Current flows down Earth wire → Fuse melts → Circuit breaks

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Stating that the earth wire 'stops' the current; candidates must understand it provides a path for current to flow to blow the fuse
    • Confusing the function of the neutral wire (completes the circuit) with the earth wire (safety only)
    • In National Grid questions, incorrectly stating that step-up transformers increase energy or power, rather than increasing potential difference to reduce current

    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

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