Q#34 (Past Exam Paper – June 2016 Paper 11 Q16)
Some gas in a cylinder is supplied with thermal energy q.
The gas does useful work in expanding at constant pressure p from volume V0 to volume VF, as shown.
Which expression gives the efficiency of this change?
Solution:
Answer: C.
The gas is supplied with thermal energy q.
(Input) thermal energy = q
Work done by expanding gas = pΔV
Work done by expanding gas = p × (Vfinal – Vinitial) = p (VF – VO)
This is the output energy.
Output energy = p (VF – VO)
Efficiency = output energy / input energy
Efficiency = p (VF – VO) / q
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