A wire PQ is made of three different materials, with resistivities ρ, 2ρ and 3ρ. There is a current I in this composite wire, as shown. [Figure showing a wire PQ composed of three segments with resistivities ρ, 2ρ, 3ρ respectively.] Which graph best shows how the potential V along the wire varies with distance x from P?
✓ Correct Answer
The correct answer is B: Graph showing potential V decreasing piecewise linearly with distance x, with three segments of increasing negative gradient (magnitude of slope).
📋 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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