A-LevelPhysicsD.C. circuitsOct/Nov 2019Paper 1 Q351 Mark
A battery has an electromotive force (e.m.f.) E and internal resistance r. The battery delivers a current I to a variable resistor and the potential difference (p.d.) across its terminals is V. [Figure showing a battery with e.m.f. E and internal resistance r connected to a variable resistor, with current I and terminal p.d. V indicated.] The variable resistor is adjusted so that I increases. Why does V decrease?
AThe e.m.f. E decreases.
BThe internal resistance r increases.
CThe p.d. across r increases.
DThe resistance of the variable resistor increases.
✓ Correct Answer
The correct answer is C: The p.d. across r increases.
📋 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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