Find the efficiency of the reversible engine, whose cycle is shown in the above T - S plot :

Formula for efficiency η=Qs−QRQs…....(1)Where QS is heat supplied and QR is heat rejected.∵ΔG=ΔH−TΔS and G is a state function. Therefore, change in enthalpy which is equal to heat supplied under constant pressure will be equal to area under curve.From the diagram, QS is area under the sloping line=12×2So−So×2To−To+2So−So×To=32SoToand QR is area under the horizontal line=2So−So×To=SoToNow substituting the value of QS and QR in (1) we get,η=32SoT0−S0To32S0T0