A student uses a joulemeter to investigate the energy used by two identical resistors connected in series with a battery. The student then reconnects the same two resistors in parallel with the same battery and repeats the investigation over the same time period. Explain why the resistors connected in parallel use more total energy than when they are connected in series.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
In the parallel arrangement each resistor experiences the full battery voltage, whereas in series the voltage is divided between the two resistors.
The equivalent resistance of the parallel circuit is lower than that of the series circuit.
A lower total resistance causes a larger current to flow from the battery.
Higher current (and the same voltage) gives a greater power (P=IV), so more energy is transferred in the same time period.
The equivalent resistance of the parallel circuit is lower than that of the series circuit.
A lower total resistance causes a larger current to flow from the battery.
Higher current (and the same voltage) gives a greater power (P=IV), so more energy is transferred in the same time period.
Examiner tips
- Use the command word ‘Explain’ – give a clear cause‑effect chain.
- Show the voltage difference between series and parallel.
- Mention the change in total resistance and its effect on current.
- Relate current and voltage to power and energy.
Common mistakes
- Confusing voltage across each resistor in series with total voltage.
- Failing to state that the total resistance is lower in parallel.
- Not linking the larger current to higher power and energy usage.
Mark scheme (4 marks)
- In parallel, each resistor has the full battery voltage across it (whereas in series the voltage is shared/split between the two resistors).
- The total resistance of the parallel circuit is less than the total resistance of the series circuit.
- A lower total resistance means a larger current is drawn from the battery in the parallel circuit.
- Greater current (and/or greater voltage) means more energy is transferred per second / power is greater, so more energy is used in the same time.
Key terms in this question
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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