A progressive longitudinal sound wave moves through air. The diagram shows the positions of the air particles along part of the wave at one instant. [Figure 24.1] Point Q is a distance x from point P. Which graph shows the variation of the displacement of the air particles with distance from P along the wave?
✓ Correct Answer
The correct answer is C: Displacement-distance graph starting at zero, increasing to a positive maximum, decreasing through zero to a negative minimum, then increasing back to zero, completing one full cycle (starts positive).
📋 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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