Assignment 5 (due before midnight of 24th Decemeber)
1. The P-V diagram below represents the states of an ideal gas during one cycle of operation of
a reversible heat engine. The cycle consists of the following 4 processes
Process
Nature of process
AB
Constant temperature (Th = 500K)
BC
Adiabatic
CD
Constant temperature (Tc = 200K)
DA
adiabatic
During process AB, the volume of the gas increases from Vo to 2Vo and the gas absorbs 1 kJ
of heat
a) If the pressure at A is Po, what is the pressure at B?
b) Determine the work performed on the gas during process AB.
c) From A to C, what is the change of entropy?
d) Calculate the heat Qc given off b the gas in process CD
e) During the full cycle of ABCDA, is the total work performed on the gas by its
surroundings positive, negative or zero? Justify your answer.
f) Sketch the temperature (T) as a function of entropy (S) for this heat cycle.
2. In he cyclic process shown below, process A to B increases the pressure of the system by 3
times, the process from B to C is adiabatic. At point A, the volume of the system is Vo.
Assuming the working as in the engine is monatomic.
a) Compute the maximum thermal efficiency of this engine.
b) Calculate the entropy change of each process and show that the entropy change of full
cycle is 0.
c) sketch the temperature (T) as a function of entropy (S) for this engine cycle based on the
parameters found in b).
