Consider a thermodynamic system that is taken through a closed sequence of processes so that it finally returns to its initial state.
(i) Define a cyclic process.
(ii) Explain, using the relation between small changes in internal energy, heat and work, why the algebraic sum of heat exchanged over one complete cycle equals the algebraic sum of work done by the system.
(iii) A student claims that an engine operating in a closed cycle can deliver positive net work output even if every individual process in the cycle is adiabatic. Examine the claim and give a reasoned answer.