A student has a circuit containing a battery and two lamps connected in series. She then reconnects the same two lamps so that they are in parallel with each other, keeping the same battery. Describe how the brightness of each lamp and the total current drawn from the battery change when moving from the series to the parallel arrangement. Explain why these changes occur.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Each lamp is brighter in the parallel arrangement than in the series arrangement.
In parallel each lamp has the full battery voltage across it, whereas in series the voltage is divided between the two lamps.
The total current drawn from the battery is greater in the parallel arrangement.
In a parallel circuit each lamp provides a separate path for current, so the total current from the battery is the sum of the currents through each branch.
In the series arrangement the current is the same through both lamps and the voltage is shared, so each lamp receives less than the full battery voltage and therefore less power.
In parallel each lamp has the full battery voltage across it, whereas in series the voltage is divided between the two lamps.
The total current drawn from the battery is greater in the parallel arrangement.
In a parallel circuit each lamp provides a separate path for current, so the total current from the battery is the sum of the currents through each branch.
In the series arrangement the current is the same through both lamps and the voltage is shared, so each lamp receives less than the full battery voltage and therefore less power.
Examiner tips
- Use the command words ‘describe’ and ‘explain’ – list the changes first, then give the reason.
- Mention voltage division in series and equal voltage in parallel.
- Show that power ∝ V²/R to justify brightness.
- Keep sentences short and use exam‑style terminology.
Mark scheme (5 marks)
- Each lamp is brighter in the parallel arrangement than in the series arrangement
- In parallel, each lamp has the full battery voltage across it (whereas in series the voltage is shared)
- The total current drawn from the battery is greater in the parallel arrangement
- In a parallel circuit, each lamp provides a separate path for current, so the total current from the battery is the sum of the currents through each branch
- In the series arrangement the current is the same throughout the circuit and the voltage is shared, so each lamp receives less than the full battery voltage / less power
Key terms in this question
series · parallel · current · brightness
Related
- All Eduqas A-Level Physics revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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