Series Circuits

    OCR
    GCSE

    Series circuits are defined by a single closed loop in which the current is the same value at any point, obeying the conservation of charge. The total potential difference supplied by the source is shared between components, directly proportional to their individual resistances. The total resistance of the circuit is the sum of the resistance of each component; consequently, adding resistors in series increases total resistance and decreases the circuit current. Mastery of these principles allows for the calculation of component parameters using Ohm's Law and the analysis of energy transfer within the system.

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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 current is the same at all points in a series circuit
    • Award 1 mark for calculating total resistance by summing individual component resistances (R_total = R1 + R2...)
    • Credit responses that apply V = IR to specific components using the potential difference across *that* component, not the supply voltage
    • Award 1 mark for explaining that adding a resistor in series increases total resistance and decreases circuit current (assuming constant supply voltage)
    • Credit the correct drawing of a circuit diagram with components connected in a single loop with no branches

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly calculated total resistance, but check which voltage value you used—was it the supply V or the component V?"
    • "Good recall of the current rule. Now explain *why* the current decreases when another lamp is added."
    • "Your calculation is correct, but you lost a mark for not showing the rearrangement of the formula first."
    • "Excellent analysis of the potential divider effect. To secure the top mark, explicitly state the relationship between resistance and voltage share."

    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 series circuit
    • Award 1 mark for calculating total resistance by summing individual component resistances (R_total = R1 + R2...)
    • Credit responses that apply V = IR to specific components using the potential difference across *that* component, not the supply voltage
    • Award 1 mark for explaining that adding a resistor in series increases total resistance and decreases circuit current (assuming constant supply voltage)
    • Credit the correct drawing of a circuit diagram with components connected in a single loop with no branches

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When analyzing circuit changes, use the logical chain: Total Resistance → Total Current → Voltage across specific components
    • 💡Annotate the circuit diagram with all known values (V, I, R) before attempting calculations to avoid selecting the wrong variable
    • 💡For 'Show that' questions involving calculations, you must show the formula, substitution, and final answer to gain full credit

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Believing current is 'used up' by components, leading to answers where current is lower after a resistor
    • Incorrectly applying the parallel voltage rule (V is same) to series circuits, rather than sharing the potential difference
    • Using the total supply voltage (V_total) with the resistance of a single component when calculating current
    • Failing to convert units (e.g., mA to A or kΩ to Ω) before substitution into equations

    Study Guide Available

    Comprehensive revision notes & examples

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    Key Terminology

    Essential terms to know

    Conservation of current in a single loop
    Distribution of potential difference (Kirchhoff's Second Law)
    Summation of resistance
    Application of Ohm's Law in series contexts

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    Explain
    Determine
    Draw
    Show

    Practical Links

    Related required practicals

    • •{"code":"PAG 3","title":"Investigation of resistance in series and parallel circuits","relevance":"Experimental verification of resistance rules"}
    • •{"code":"PAG 4","title":"I-V Characteristics","relevance":"Measuring V and I for components in series"}

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