A cell of electromotive force (e.m.f.) E and internal resistance r is connected to a variable resistor, as shown. [Figure 34.1] The resistance of the variable resistor is gradually increased from r to 3r. Which graph shows the variation of the potential difference (p.d.) v across the internal resistance with the p.d. V across the variable resistor?
✓ Correct Answer
The correct answer is A: Graph of v vs V, starts at (0, E/2) and ends at (3E/4, E/4), straight line with negative gradient
📋 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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