We can imagine two different energy sources with the same initial internal energy, one large source initially at an intermediate temperature and one smaller source initially at a higher temperature. Which energy source should we choose if we want to maximize the work output as the energy source equilibrates with the energy sink (TH → TL)? Consider a Carnot heat engine placed between a finite thermal energy source and an infinite thermal energy sink. Since the temperature of the thermal source is constantly changing, then so must the efficiency of the Carnot engine. We need to capture the effects of this ever-changing Carnot efficiency. To do this, we will develop an expression for every differential amount of work produced by the Carnot engine then sum all these differential amounts of work together (i.e., integrate) to calculate the total net work produced during the equilibrating process. How is the differential net work output (δWnet,out) of the Carnot engine related to each differential amount of heat supplied to the engine (δQH)?