Parallel Circuits

    OCR
    GCSE

    Parallel circuits are defined by the arrangement of components in separate branches, creating multiple paths for electrical current to flow. In this configuration, the potential difference across each branch is identical to the source voltage, ensuring independent operation of components. The total current drawn from the power supply is the sum of the currents through individual branches, consistent with the conservation of charge (Kirchhoff's First Law). Furthermore, the total resistance of a parallel circuit is always less than the resistance of the smallest individual resistor, a critical concept for analyzing load and power distribution in domestic wiring.

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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 the potential difference across each branch is equal to the source potential difference
    • Award 1 mark for calculating total current by summing the individual currents in each branch (conservation of charge)
    • Credit responses that explain that adding a resistor in parallel decreases the total resistance of the circuit
    • For Higher Tier: Award marks for correct substitution into the reciprocal formula (1/R_total = 1/R1 + 1/R2) and correctly inverting the final answer

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly identified that voltage is the same, but you applied the series rule for resistance. Remember: more branches = easier flow"
    • "Don't forget the final step in your resistance calculation: 1/Rt is not the answer, you must find Rt"
    • "Good calculation of the branch currents. To get full marks, explicitly show the sum of these equals the supply current"
    • "Your explanation of independent switching is correct; now extend this to discuss the brightness of the bulbs compared to a series circuit"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that the potential difference across each branch is equal to the source potential difference
    • Award 1 mark for calculating total current by summing the individual currents in each branch (conservation of charge)
    • Credit responses that explain that adding a resistor in parallel decreases the total resistance of the circuit
    • For Higher Tier: Award marks for correct substitution into the reciprocal formula (1/R_total = 1/R1 + 1/R2) and correctly inverting the final answer

    Examiner Tips

    Expert advice for maximising your marks

    • 💡In multiple-choice questions, remember that the total resistance in parallel is always less than the smallest individual resistor—use this to eliminate incorrect options quickly
    • 💡When calculating total resistance on the Higher tier, write down the formula '1/Rt = 1/R1 + 1/R2' explicitly before substituting to secure method marks even if the arithmetic fails
    • 💡If asked to explain why lights in a house are wired in parallel, focus on two points: independent switching and maintaining full voltage (brightness) across all lamps

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Applying series circuit rules to parallel contexts, specifically adding resistances (R = R1 + R2) instead of using the reciprocal method
    • Assuming current is the same in all branches regardless of the resistance of the components in those branches
    • Forgetting to invert the value of 1/R_total at the end of the calculation to find R_total
    • Stating that voltage 'splits' across parallel branches rather than remaining constant

    Study Guide Available

    Comprehensive revision notes & examples

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    Key Terminology

    Essential terms to know

    Uniformity of potential difference across branches
    Current splitting and conservation of charge
    Calculation of effective resistance in parallel
    Independence of components and fault tolerance

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    Explain
    State
    Compare
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    Practical Links

    Related required practicals

    • •{"code":"PAG P3","title":"Investigation of resistance","relevance":"Comparing total resistance in series vs parallel arrangements"}

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