Final answer:
The work done by a heat engine is the difference between the heat added to the system (Qh) and the heat released (Qc), which is captured by the equation W = Qh - Qc. This work is the useful energy output of the engine.
Step-by-step explanation:
The work done by a heat engine is described by the difference between the heat coming in and the heat flowing out. In a cyclical process of a heat engine, the net work (W) done by the system is equal to the net heat transferred into the system. This relationship is represented by the equation W = Qh - Qc, where Qh represents the heat transfer from the hot object (hot reservoir) and Qc is the heat transfer into the cold object (cold reservoir).
Thus, option 'B' is correct as it states that the work done by a heat engine is the difference between the heat coming in and the heat flowing out.An engine's efficiency can be expressed by the ratio of work output divided by the amount of energy input.
Both heat transfer, denoted as Q, and work, denoted as W, are ways of bringing energy into or taking energy out of a system, and they both can affect the internal energy (U) of the system. However, heat and work do not get stored as such in a system; instead, they bring about changes such as a temperature increase.