A-LevelPhysicsThermodynamicsFeb/Mar 2017Paper 1 Q171 Mark
A gas is enclosed inside a cylinder which is fitted with a frictionless piston. [Figure showing a piston in a cylinder with gas, initial volume V₁, external pressure p, final volume V₂] Initially, the gas has a volume V₁ and is in equilibrium with the external pressure p. The gas is then heated slowly so that it expands at constant pressure, pushing the piston back until the volume of the gas has increased to V₂. How much work is done by the gas during this expansion?
Ap (V₂ - V₁)
B½ p (V₂ - V₁)
Cp (V₂ + V₁)
D½ p (V₂ + V₁)
✓ Correct Answer
The correct answer is A: p (V₂ - V₁)
📋 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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