A 12 V battery is connected to two resistors in series. One resistor has a potential difference of 4 V across it. Explain how the potential differences are distributed across the two resistors and describe how this distribution would change if the resistors were reconnected in parallel instead.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A 12 V battery is connected to two resistors in series. The potential difference across one resistor is measured as 4 V.
Model answer (4 marks)
In a series circuit the voltage drops across the two resistors add to the supply voltage, so the second resistor has 12 V − 4 V = 8 V across it. The larger the resistance, the larger the voltage drop.
If the same two resistors were wired in parallel they would each experience the full supply voltage of 12 V; the voltage across each resistor would be the same and would not be divided between them.
If the same two resistors were wired in parallel they would each experience the full supply voltage of 12 V; the voltage across each resistor would be the same and would not be divided between them.
Examiner tips
- Show the 4 V + 8 V = 12 V calculation for series
- State that the larger resistor has the larger drop
- Explain that in parallel both resistors see the same 12 V
Common mistakes
- Saying the voltage is split equally in series
- Confusing current with voltage in parallel
Mark scheme (4 marks)
- In series, the potential differences across the components add up to the total supply potential difference (12 V), so the second resistor has 8 V across it.
- In series, the resistor with the higher resistance has a greater potential difference across it.
- In parallel, both resistors have the same potential difference across them.
- In parallel, each resistor has the full supply potential difference (12 V) across it, so neither resistor shares the voltage.
Key terms in this question
potential difference · series · parallel
Related
- All Pearson Edexcel International GCSE Physics (4PH1) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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