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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