Answers to Objective Questions

Abstract

Answer (b). The work done on a gas equals the area under the process curve in a PV diagram. In an isobaric process, the pressure is constant, so P f = P i and the work done is the area under curve 1-2 in ANS. FIG. OQ20.1. For an isothermal process, the ideal gas law gives P f V f = P i V i , so P f = (V i /V f) P i = 2P i and the work done is the area under curve 1-3 in ANS. FIG. OQ20.1. For an adiabatic process, P f V f γ = P i V i γ = constant (see Ch. 21), so P f = (V i V f) γ P i and P f = 2 γ P i > 2P i since γ > 1 for all ideal gases. The work done in an adiabatic process is the area under curve 1-4, which exceeds that done in either of the other processes.