A-LevelPhysicsD.C. circuitsFeb/Mar 2025Paper 1 Q361 Mark
A cell of electromotive force (e.m.f.) E and internal resistance r is connected in series with a switch S and an external resistor of resistance R. [Figure 36.1] The potential difference (p.d.) between P and Q is V. Which statement is correct when S is changed from open to closed?
AV increases because there is a p.d. across R.
BV decreases because there is a p.d. across r.
CV remains the same because the decrease of p.d. across r is balanced by the increase of p.d. across R.
DV remains the same because the sum of the p.d.s across r and R is still equal to E.
✓ Correct Answer
The correct answer is B: V decreases because there is a p.d. across r.
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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