The initial state of a certain gas is (pi, Vi, Ti). It undergoes expansion till its volume becomes Vf. Consider the following two cases:

(a) the expansion takes place at a constant temperature. 

(b) the expansion takes place at constant pressure.

 
Plot the p-V diagram for each case. In which of the two cases, is the work done by the gas more?

Hint: The processes are isothermal and isobaric processes.
Step 1: Draw the graphs of isothermal and isobaric processes.
Consider the diagram p-V, where variation is shown for each process.
Process 1 is isobaric and process 2 is isothermal.
Step 2: Find the work done in two processes.
Since the work done = area under the p-V curve. Here, the area under the p-V curve 1 is more. So, the work done is more when the gas expands in the isobaric process.