Series and parallel circuits

    AQA
    GCSE

    Series and parallel circuits are defined by the distinct conservation laws governing current and potential difference. Candidates must apply the principle that current is conserved in series but splits in parallel, while potential difference is shared in series but remains constant across parallel branches. Mastery requires the integration of Ohm’s Law (V=IR) to calculate unknowns and a precise understanding of effective resistance: adding resistors increases total resistance in series but decreases it in parallel. Analysis must extend to the dynamic effects of changing component resistance on the entire circuit.

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    Objectives
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    Exam Tips
    4
    Pitfalls
    4
    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating that current is the same at all points in a single closed loop of a series circuit
    • Award 1 mark for calculating total resistance in series by summing individual resistance values (R_total = R1 + R2)
    • Credit responses that explain that adding a resistor in parallel decreases total resistance because it provides an additional path for charge flow
    • Award 1 mark for recognizing that the potential difference across each component in a parallel arrangement is equal to the source potential difference
    • Award 1 mark for applying V = IR correctly to a specific component rather than the whole circuit when data is localized

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that current is the same at all points in a single closed loop of a series circuit
    • Award 1 mark for calculating total resistance in series by summing individual resistance values (R_total = R1 + R2)
    • Credit responses that explain that adding a resistor in parallel decreases total resistance because it provides an additional path for charge flow
    • Award 1 mark for recognizing that the potential difference across each component in a parallel arrangement is equal to the source potential difference
    • Award 1 mark for applying V = IR correctly to a specific component rather than the whole circuit when data is localized

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When asked to explain why resistance decreases in parallel, explicitly link 'more paths for current' to 'increased total current for the same p.d.' implies 'lower resistance'
    • 💡Annotate the circuit diagram with known values (V, I, R) before selecting an equation; this prevents using the wrong voltage for a specific component
    • 💡For Higher Tier, remember that if a variable resistor's resistance increases in a series circuit, it takes a larger share of the p.d., leaving less for other components

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Incorrectly summing potential differences across parallel branches instead of recognizing they are equal to the supply voltage
    • Stating that adding a resistor in parallel increases total resistance because 'there are more components', failing to recognize the increased pathway effect
    • Confusing current and potential difference rules, such as stating current is shared in series and same in parallel
    • Applying the total circuit voltage to a single component's resistance when calculating current in a series circuit

    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    Explain
    Determine
    Compare
    Draw

    Practical Links

    Related required practicals

    • •{"code":"Required Practical 3","title":"Resistance","relevance":"Investigating how resistance of wire combinations changes in series vs parallel"}
    • •{"code":"Required Practical 4","title":"I-V Characteristics","relevance":"Constructing circuits to measure I and V across components"}

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