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Monday, November 11, 2019

Some gas in a cylinder is supplied with thermal energy q.


Question 34
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?






Reference: Past Exam Paper – June 2016 Paper 11 Q16





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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