http://wps.prenhall.com/esm_giancoli_physicsppa_6/0,8713,1115091-,00.html (under practice questions) On questions 16,17, & 18 I'm trying to figure what is the difference between them (Clearly Tc is different, but how does that change the problem?). The question asks The heat engine shown above is a) a reversible (Carnot) heat engine. b) an irreversible (Carnot) heat engine. c) a hoax. d) none of the above. I'm guessing I just don't understand the concepts, as I thought a Carnot engine was suppose to avoid irreversible processes, like an idealization. Anyway, the answer to 17 & 18 are "a hoax." They all seem to have thermal efficiencies of less than 1, so how should I look at these questions?