A student connects two resistors in series with a battery. The student then reconnects the same two resistors in parallel with the same battery. Describe how the total resistance of the circuit and the total current from the battery change when the student switches from a series connection to a parallel connection. Explain why these changes occur.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The total resistance of the circuit decreases when the resistors are moved from series to parallel.
In a parallel arrangement each resistor offers its own separate path for the current, so the overall resistance is less than the smallest individual resistance.
Consequently the total current supplied by the battery increases.
Because the battery’s potential difference remains unchanged, a lower resistance means a higher current according to V=IR (or equivalent reasoning).
In a parallel arrangement each resistor offers its own separate path for the current, so the overall resistance is less than the smallest individual resistance.
Consequently the total current supplied by the battery increases.
Because the battery’s potential difference remains unchanged, a lower resistance means a higher current according to V=IR (or equivalent reasoning).
Examiner tips
- Use the command word ‘describe’ – give a short explanation, not a long essay.
- Show the relationship V=IR to justify the increase in current.
- Mention that the smallest resistance dominates the parallel resistance.
- Keep the answer concise – 4 marks only.
Common mistakes
- Confusing series and parallel relationships – writing that resistance increases in parallel.
- Forgetting to state that the battery voltage stays the same.
- Using vague terms like ‘more current’ without linking to V=IR.
Mark scheme (4 marks)
- Total resistance decreases when resistors are changed from series to parallel
- In parallel, each resistor provides its own separate path for current, so overall resistance is less than the smallest individual resistance
- Total current from the battery increases when changed from series to parallel
- Because the potential difference (voltage) from the battery stays the same but the total resistance is lower, so current increases (linking to V = IR or equivalent reasoning)
Key terms in this question
resistance · current · series · parallel
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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