Consider two actual power plants operating with solar energy. Energy is supplied to one plant from a solar pond at 80°C and to the other from concentrating collectors that raise the water temperature to 600°C. Which of these power plants will have a higher efficiency? Explain.

A heat engine running backward is called a refrigerator if its purpose is to extract heat from a cold reservoir. The same engine running backward is called a heat pump if its purpose is to exhaust warm air into the hot reservoir. Heat pumps are widely used for home heating. You can think of a heat pump as a refrigerator that is cooling the already cold outdoors and, with its exhaust heat QH, warming the indoors. Perhaps this seems a little silly, but consider the following. Electricity can be directly used to heat a home by passing an electric current through a heating coil. This is a direct, 100% conversion of work to heat. That is, 19.0 kW of electric power (generated by doing work at the rate 19.0 kJ/s at the power plant) produces heat energy inside the home at a rate of 19.0 kJ/s. Suppose that the neighbor's home has a heat pump with a coefficient of performance of 3.00, a realistic value. NOTE: With a refrigerator, "what you get" is heat removed. But with a heat pump, "what you…

A window conducts power from a house to the cold outdoors. What power is conducted through a window of twice the area? Be specific 4x, 2x, the same, ½ x, ¼ x, etc. Explain your answer.

Why do refrigerators, air conditioners, and heat pumps operate most costeffectively for cycles with a small difference between Th and Tc? (Note that the temperatures of the cycle employed are crucial to its COP.)

We ordinarily say that U=0 for an isothermal process. Does this assume no phase change takes place? Explain your answer.

. The temperature in the deep interiors of some giant molecular clouds in the Milky Way galaxy is 50 K. Compare the amount of energy that would have to be transferred to this environment to the amount that would have to transferred to a room temperature environment to bring about a 1.0 J/K increase in the entropy of the universe in each case.

Are the entropy changes of the system in the following processes positive or negative? (a) water vapor that condenses on a cold surface; (b) gas in a that leaks into the surrounding atmosphere; (c) an ice cube that melts in a glass of lukewarm water; (d)the lukewarm water of part (c); a real heat engine performing a cycle; (f) food cooled in a refrigerator.

Use a PV diagram such as the one in Figure 22.2 (page 653) to figure out how you could modify an engine to increase the work done.

An engine absorbs three times as much heat as it discharges. The work done by the engine per cycle is 50 J. Calculate (a) the efficiency of the engine, (b) the heat absorbed per cycle, and (c) the heat discharged per cycle.