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, 20.0 \rm kW of electric power (generated by doing work at the rate 20.0 kJ/s at the power plant) produces heat energy inside the home at a rate of 20.0 kJ/s. Suppose that the neighbor's home has a heat pump with a coefficient of performance of 7.00, a realistic value. NOTE: With a refrigerator, "what you get" is heat removed. But with a heat pump, "what you get" is heat delivered. So the coefficient of performance of a heat pump is K=QH/Win. An average price for electricity is about 40 MJ per dollar. A furnace or heat pump will run typically 300 hours per month during the winter. What does one month's heating cost in the home with a 16.0 kW electric heater? What does one month's heating cost in the home of a neighbor who uses a heat pump to provide the same amount of heating?
Wavelength is the distance between from one crest to another crest or from one trough to another trough. The amplitude is the distance from the midpoint to the crest or trough. Crest is the highest point of the or a wave. Tough is the lowest point of the or a wave. Rest position is the position where it lies on the midpoint line.
