Current

    OCR
    GCSE

    Electric current is defined as the rate of flow of electrical charge, measured in Amperes (A) using an ammeter connected in series. In metallic conductors, charge carriers are delocalized electrons, though conventional current is defined as flowing from positive to negative potential. Candidates must apply the relationship I = Q/t and analyze current distribution in series and parallel circuits, adhering to the conservation of charge (Kirchhoff's First Law). Distinction between direct current (d.c.) produced by cells and alternating current (a.c.) from mains supply is fundamental to circuit analysis.

    0
    Objectives
    3
    Exam Tips
    4
    Pitfalls
    5
    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for defining current specifically as the 'rate of flow of charge' (not just flow of electrons).
    • Credit calculations using I = Q / t where time is correctly converted to seconds.
    • Award 1 mark for stating that current is the same at all points in a series circuit.
    • Credit the application of Kirchhoff's First Law: the sum of currents entering a junction equals the sum leaving it.
    • Award 1 mark for drawing or describing an ammeter connected in series with the component.

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly calculated the value, but forgot to convert minutes to seconds. Always check your units first."
    • "You stated current decreases after the resistor. Remember, current is conserved—it is not used up, only energy is transferred."
    • "Good use of the equation. To improve, explicitly state the rearrangement step before substituting the numbers."
    • "You identified the parallel branches correctly. Now explain how the resistance of each branch affects the proportion of current flowing through it."

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for defining current specifically as the 'rate of flow of charge' (not just flow of electrons).
    • Credit calculations using I = Q / t where time is correctly converted to seconds.
    • Award 1 mark for stating that current is the same at all points in a series circuit.
    • Credit the application of Kirchhoff's First Law: the sum of currents entering a junction equals the sum leaving it.
    • Award 1 mark for drawing or describing an ammeter connected in series with the component.

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Always look for the prefix 'm' (milli) in current values; you must divide by 1000 to convert mA to A before calculation.
    • 💡When explaining why current splits in parallel, explicitly reference the 'conservation of charge'.
    • 💡In circuit diagrams, trace the loop with your finger to confirm if components are in series (one path) or parallel (branching paths).

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Stating that current is 'used up' or decreases after passing through a resistor in a series circuit.
    • Failing to convert time from minutes or hours into seconds before substituting into Q = It.
    • Confusing the direction of conventional current (positive to negative) with electron flow (negative to positive).
    • Connecting ammeters in parallel across a component instead of in series.

    Study Guide Available

    Comprehensive revision notes & examples

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    Key Terminology

    Essential terms to know

    Rate of flow of charge (I = Q/t)
    Current behavior in series vs. parallel circuits
    Conventional current vs. electron flow
    Direct Current (d.c.) vs. Alternating Current (a.c.)
    Measurement using ammeters

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    State
    Explain
    Draw
    Describe

    Practical Links

    Related required practicals

    • •{"code":"PAG P3","title":"Investigation of resistance","relevance":"Requires accurate measurement of current using ammeters in series to determine resistance."}
    • •{"code":"PAG P4","title":"Series and parallel circuits","relevance":"Direct investigation of how current behaves in different circuit configurations."}

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