A set of fairy lights is wired in series. When one bulb breaks and stops conducting, all the other bulbs go out. A student suggests that rewiring the fairy lights in parallel would solve this problem. Explain why the student's suggestion is correct.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Fairy lights are commonly used as decorative lighting. Older sets were wired in series, meaning a single broken bulb caused the entire set to stop working.
Model answer (4 marks)
In a series circuit there is only one path for current to flow. A broken bulb creates a gap, so no current flows through the circuit and all bulbs go out. In a parallel circuit each bulb has its own separate path or branch for current. If one bulb breaks, current can still flow through the other branches, so the remaining bulbs stay on.
Examiner tips
- Use the term ‘single path’ for series and ‘separate branches’ for parallel.
- Explain the effect of a break on current flow in each configuration.
Mark scheme (4 marks)
- In a series circuit there is only one path for current to flow
- A broken bulb in series creates a gap/break, so no current flows anywhere in the circuit
- In a parallel circuit each bulb has its own separate path/branch for current
- If one bulb breaks in parallel, current can still flow through the other branches, so the remaining bulbs stay on
Related
- All OCR GCSE Physics A: Gateway Science (J249) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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