The graph given below shows the total work done in an expansion when the state of an ideal gas is changed reversibly and isothermally from (Pi,Vi) to (Pf,Vf). Compare the work done in the above case with that carried out against a constant external pressure Pf.
(i) Area ABVfVi represents total work done for a reversible isothermal expansion from (Pi,Vi) to (Pf,Vf).
(ii) Area CBVfVi represents work done against a constant pressure Pf.