A student connects two identical lamps in parallel with a battery. Explain why the total resistance of the parallel circuit is less than the resistance of a single lamp, and describe what happens to the current from the battery compared to when only one lamp is connected.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Two identical lamps are connected in parallel with a battery. Each lamp has a resistance of 6 Ω.
Model answer (4 marks)
In a parallel circuit the battery is connected to two branches, so the current can flow through either lamp.
Because there are two paths, charge can move more easily – the effective resistance is lower than that of a single lamp.
Consequently the battery supplies a larger total current. The total current equals the sum of the currents through each lamp, i.e. the current splits between the two branches.
Because there are two paths, charge can move more easily – the effective resistance is lower than that of a single lamp.
Consequently the battery supplies a larger total current. The total current equals the sum of the currents through each lamp, i.e. the current splits between the two branches.
Examiner tips
- Show the two branches explicitly; mention that current splits.
- Explain that lower resistance means easier flow, leading to higher total current.
- Use the phrase ‘total current equals the sum of the branch currents’ to hit the mark.
Common mistakes
- Saying the resistance is higher instead of lower.
- Claiming the current is the same for both lamps without explaining the split.
- Using the wrong units or not recognising that the battery current increases.
Mark scheme (4 marks)
- In a parallel circuit, the current has more than one path/branch to flow through
- Because there are multiple paths, it is easier for charge to flow, so the total resistance is lower than a single lamp alone
- The current from the battery is greater when two lamps are connected in parallel compared to one lamp alone
- The total current from the battery equals the sum of the currents through each lamp / the current splits between the two branches
Key terms in this question
parallel · resistance · current
Related
- All Edexcel GCSE Physics (1PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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