Power

    AQA
    GCSE

    Power is rigorously defined as the rate at which energy is transferred or the rate at which work is done. It quantifies the speed of energy conversion between stores, measured in Watts (W), where one Watt represents one Joule per second. The concept bridges mechanical systems, where power relates to force and velocity, and electrical systems, where it relates to potential difference and current. Mastery involves applying formulae for mechanical and electrical power, converting between units such as kilowatts and Watts, and evaluating the efficiency of energy transfer in practical contexts.

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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 defining power as 'rate of energy transfer' or 'rate of doing work' - 'amount of energy over time' is insufficient.
    • Credit correct substitution into P = E/t, ensuring time is converted to seconds (s) before calculation.
    • Award 1 mark for selecting P = I^2 R when current is the known constant variable in series circuits.
    • Candidates must state the unit as Watts (W) or Joules per second (J/s) to gain the final accuracy mark.

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for defining power as 'rate of energy transfer' or 'rate of doing work' - 'amount of energy over time' is insufficient.
    • Credit correct substitution into P = E/t, ensuring time is converted to seconds (s) before calculation.
    • Award 1 mark for selecting P = I^2 R when current is the known constant variable in series circuits.
    • Candidates must state the unit as Watts (W) or Joules per second (J/s) to gain the final accuracy mark.

    Examiner Tips

    Expert advice for maximising your marks

    • šŸ’”Always check if the question asks for 'energy transferred' (Joules) or 'power' (Watts); these are frequently confused in multi-step calculations.
    • šŸ’”For Higher Tier, be prepared to combine power formulae with efficiency: calculate total input power first before applying the efficiency percentage.
    • šŸ’”When asked to compare two motors, explicitly reference the 'time taken' to do the same work; the one with the shorter time has the greater power.

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Failing to convert time from minutes or hours into seconds before substituting into P = E/t.
    • Confusing 'power' with 'energy' in qualitative explanations, stating a more powerful motor does 'more work' rather than doing work 'faster'.
    • Using the supply voltage instead of the potential difference across the specific component when calculating electrical power using P = VI.

    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

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    Practical Links

    Related required practicals

    • ā€¢{"code":"Required Practical 1","title":"Specific Heat Capacity","relevance":"Calculating the power of the immersion heater using P = VI to determine energy supplied."}

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