A thermodynamics cycle similar to Carnot's is constructed with four reversible steps:

1. Reversible isothermal expansion from P1, V1, Th to P2, V2, Th

2. Reversible adiabetic expansion from P2, V2, Th to P3, V2, Tc

3. Reversible isothermal compression from P3, V2, Tc to P4, V1, Tc

4. Reversible adiabatic compression from P4, V1, Tc to P1, V1, Th

Find an expression for the efficiency if the working fluid is an ideal gas with Cv its constant volume heat capacity.