Explain what happens to the current in a circuit when the resistance is increased, and use the concept of potential difference to explain why this occurs.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A student has a simple circuit containing a battery, a variable resistor, and an ammeter. The student gradually increases the resistance of the variable resistor while keeping the battery the same.
Model answer (4 marks)
Current decreases as the resistance of the variable resistor is increased.
The battery supplies a fixed potential difference, so the voltage across the circuit does not change.
According to Ohm’s law, I = V/R – the current is proportional to the potential difference and inversely proportional to resistance. With V constant, increasing R reduces I.
The potential difference is the driving force that pushes charges through the circuit; a larger resistance offers more opposition, so fewer charges pass per second, lowering the current.
The battery supplies a fixed potential difference, so the voltage across the circuit does not change.
According to Ohm’s law, I = V/R – the current is proportional to the potential difference and inversely proportional to resistance. With V constant, increasing R reduces I.
The potential difference is the driving force that pushes charges through the circuit; a larger resistance offers more opposition, so fewer charges pass per second, lowering the current.
Examiner tips
- State the relationship I = V/R explicitly; link V, I and R. Explain that V is fixed by the battery. Show that increasing R reduces I. Use the words ‘potential difference drives the charges’ to satisfy the concept requirement.
Common mistakes
- Confusing resistance with voltage – saying the voltage increases with resistance. Forgetting to mention that the battery’s potential difference is constant. Using the wrong formula (e.g., I = R/V) or omitting the inverse relationship.
Mark scheme (4 marks)
- Current decreases as resistance increases
- The potential difference of the battery stays the same / is fixed
- Correct relationship stated — current is proportional to potential difference and inversely proportional to resistance (or equivalent correct statement linking all three quantities)
- The potential difference drives the charges / provides the 'push', so with more resistance opposing the flow, fewer charges pass per second
Key terms in this question
current · potential difference · resistance
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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