A cell of internal resistance r and electromotive force (e.m.f.) E is connected in series with a resistor of resistance R. [Figure 36.1] The resistance R and the e.m.f. E remain fixed. The internal resistance r of the cell changes over time. Which graph best shows the variation of the current I in the circuit with the internal resistance r?
✓ Correct Answer
The correct answer is B: [Graph B: I vs r, current decreases as r increases, with the curve getting steeper (concave down).]
📋 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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