Two identical lamps are connected in parallel with each other and then connected to a battery. State and explain what happens to the brightness of one lamp and the current from the battery when a third identical lamp is added in parallel with the other two.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The brightness of one lamp stays the same because the potential difference across each lamp remains unchanged in a parallel circuit. The current from the battery increases because adding a lamp in parallel provides an additional path for current, reducing the total resistance of the circuit.
Examiner tips
- Use the word ‘stays the same’ for brightness, not ‘increases’ or ‘decreases’.
- Explain that the voltage across each lamp is unchanged in parallel.
- Show that the total resistance falls, so the battery current rises.
Mark scheme (4 marks)
- The brightness of one lamp stays the same / is unchanged
- Because the potential difference across each lamp remains the same / unchanged (in a parallel circuit)
- The current from the battery increases
- Because adding a lamp in parallel provides an additional path for current / reduces the total resistance of the circuit
Key terms in this question
Related
- All Cambridge International IGCSE Physics (0625) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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