A Carnot engine operates between temperature levels of 600 K and 300 K. It drives a Carnot refrigerator, which provides cooling at 250 K and discards heat at 300 K. Determine a numerical value for the ratio of heat extracted by the refrigerator ("cooling load") to the heat delivered to the engine ("heating load").

Explanation:

Formula for maximum efficiency of a Carnot refrigerator is as follows.

      ..... (1)

And, formula for maximum efficiency of Carnot refrigerator is as follows.

      ...... (2)

Now, equating both equations (1) and (2) as follows.

  =        

       

                    =

                    =

                    = 2.5

Thus, we can conclude that the ratio of heat extracted by the refrigerator ("cooling load") to the heat delivered to the engine ("heating load") is 2.5.

D. sugar changes from white to a light amber color We're looking for a chemical change. So let's examine the options and see what happening with them. A. adding cream and milk to the mixture She's just making a mixture here. No unexpected reactions or changes happen as she adds the cream and milk. So this is the wrong answer. B. mixing the sugar with water Dissolving the sugar in water. Once again, nothing unusual happens and if she were to evaporate the water, she'd be left with the original sugar. So this is the wrong answer. C. melting the sugar Just starting a simple phase change. Once again, no the right answer. D. sugar changes from white to a light amber color She's melted the sugar and has a clear fluid. As she continued to heat this fluid, it suddenly turns light amber. She has made a permanent change to the substance that she can't undo by simply physical means. She has converted part of the sugar into caramel. So a chemical change has happened here.