we have 3 identical bodies of constant thermal capacity, two at 300K and one at 100k. we want to know the highest temperature that any one of the bodies can be raised by the operation of heat engines. we already solved this problem in a tute, and we assumed the heat engines were reversible so that there was no change in entropy. The physics is confusing me, though. Why do we want our heat engines to be efficient? Surely for the max. amount of heat transfer to another body we want an inefficient heat engine so that the min. possible input heat is converted to work? thanks very much.