A heat engine using a diatomic ideal gas goes through the following closed cycle:
■ Isothermal compression until the volume is halved.
■ Isobaric expansion until the volume is restored to its initial value.
■ Isochoric cooling until the pressure is restored to its initial value.
What are the thermal efficiencies of

(a) This heat engine

(b) A Carnot engine operating between the highest and lowest temperatures reached by this engine?