The National Grid

    AQA
    GCSE

    The National Grid is defined as the system of cables and transformers linking power stations to consumers. Candidates must articulate the necessity of high-voltage transmission: step-up transformers increase potential difference to decrease current ($I = P/V$), which significantly reduces thermal energy dissipation in transmission cables ($P_{loss} = I^2 R$). Credit is awarded for linking this process to increased transmission efficiency and economic viability. Step-down transformers subsequently decrease potential difference to safe levels (230 V) for domestic use. Responses must distinguish between the roles of voltage manipulation for efficiency versus safety.

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    Objectives
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    Exam Tips
    3
    Pitfalls
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    Key Terms
    4
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for defining the National Grid as a system of cables and transformers only
    • Credit responses that state step-up transformers increase potential difference to decrease current
    • Award 1 mark for linking reduced current to reduced heating effect or energy loss in cables
    • Candidates must explain that step-down transformers reduce potential difference to a safe level (230V) for domestic use

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for defining the National Grid as a system of cables and transformers only
    • Credit responses that state step-up transformers increase potential difference to decrease current
    • Award 1 mark for linking reduced current to reduced heating effect or energy loss in cables
    • Candidates must explain that step-down transformers reduce potential difference to a safe level (230V) for domestic use

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Explicitly exclude power stations when defining the National Grid; marks are frequently lost for implying generation is part of the grid
    • 💡For explanation questions on efficiency, structure the answer logically: High PD -> Low Current -> Less thermal energy loss (referencing P=I^2R)
    • 💡When evaluating overhead vs. underground cables, use a table to ensure you cover technical, environmental, and social aspects systematically

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Incorrectly including power stations or consumers within the definition of the National Grid
    • Stating that high voltage is used to 'push' electricity faster rather than to reduce current
    • Using vague phrasing like 'electricity is lost' instead of specific terminology such as 'energy is dissipated as thermal energy'

    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

    State
    Explain
    Calculate
    Compare
    Evaluate

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