Figure is the P − V diagram for a Carnot cycle. In this diagram,
Curve DA represents isothermal process and BC adiabatic process
Curve AB represents adiabatic process and BC isothermal process
Curve CD represents isothermal process and DA adiabatic process
Curve CD represents adiabatic process and DA isothermal process
For adiabatic process, constant. Differentiating w.r.t V we get
For isothermal process, PV = constant. Hence
Now, dP/dV is the slope of the (P − V)graph. Thus the slope of the (P − V) graph for an
adiabatic process is γ times that for an isothermal process. Hence curves BC and DA
both represent adiabatic process and curves AB and CD both represent isothermal
process.