Question

Consider an ideal gas in a frictionless piston cylinder assembly. The weightless piston is initially loaded with a large number of small weights. How would you carry out a reversible isothermal expansion process? Assume that a large number very small weights and an arrangement for reversible heat transfer are available.
1. Without adding or removing weights on the piston, transfer heat to the system
2. Without adding or removing weights on the piston, transfer heat from the system
3. Adding weights on the piston, transfer heat to the system
4. Removing weights from the piston, transfer heat to the system

Answer 1

Correct Answer - Option 4 : Removing weights from the piston, transfer heat to the system

To carry out the isothermal process, the small weights will be removed from the piston one by one. When the one piece is removed it will cause the decrease in pressure and simultaneously decrease in temperature. But there will be a lot of time and the process is so small that the temperature decrease will cause the heat to flow from the surrounding to keep the temperature same and so the pressure will also remain same. Ideally, these infinite slow processes will cause the reversible isothermal process.