A-LevelPhysicsForces, density and pressureOct/Nov 2017Paper 1 Q151 Mark
Air is trapped inside a glass bulb which is immersed in water and attached to a U-tube containing mercury. The densities of water and mercury are ρw and ρm respectively. The surface of the water is open to the atmosphere where atmospheric pressure is P. [Figure showing a glass bulb with trapped air, immersed in water, connected to a U-tube with mercury, labelled with P, ρw, hw, ρm, hm] The acceleration of free fall is g. What is the pressure of the air in the glass bulb?
AP + gρw hw + gρm hm
BP + gρw hw - gρm hm
Cgρw hw + gρm hm
Dgρw hw - gρm hm
✓ Correct Answer
The correct answer is B: P + gρw hw - gρm hm
📋 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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