In a reversible process, what condition must be met regarding the system and surroundings?
**Cyclic process** system returns to initial state, ΔU=0 over cycle, net work W_net = area enclosed in P-V diagram, Q_net = W_net from first law ΔU= Q - W =0 => Q_net = W_net, clockwise cycle work done by system positive, counterclockwise work done on system negative, efficiency η = W_net/Q_in. A process is reversible if it can be reversed, returning both the system and surroundings to their original states without any net change elsewhere. This requires quasi-static conditions and no dissipative effects like friction. Using first law ΔU = Q - W, W = ∫ P dV, isobaric W = P ΔV, isothermal W
Ref: NCERT > Physics Book > Thermodynamics > Cyclic Processes and Reversibility Concepts