O-LevelPhysicsThermal PhysicsOct/Nov 2025Paper 1 Q221 Mark
Air is trapped in a glass tube by a liquid. When the tube is horizontal, the length of the trapped air is 50 mm and its pressure is 1.0 × 10⁵ Pa. [Figure 22.1] When the tube is vertical, with the closed end downwards, the length of the trapped air is 45 mm. The temperature of the air remains constant. What is the pressure of the trapped air when the tube is vertical?
A0.50 × 10⁵ Pa
B0.90 × 10⁵ Pa
C1.1 × 10⁵ Pa
D1.9 × 10⁵ Pa
✓ Correct Answer
The correct answer is C: 1.1 × 10⁵ Pa
📋 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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