Which statement is true?
A. Light waves always travel at a constant speed, but sound waves do not.
B. Waves travel at different speeds through different materials.
C. Light waves and sound waves travel at the same constant speed.
D. Wave speed depends on the amplitude of the wave.

Where do most of the visible electromagnetic waves on Earth come from?
A. X-rays
B. radio waves
C. the sun
D. fluorescent lights

Yellow light and blue light are two examples of electromagnetic radiation from the sun. Which statement correctly compares yellow light and blue light?
A. They have the same wavelength.
B. They are both types of ultraviolet light.
C. They are both types of visible light.
D. They travel at different speeds.

Aheat 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 \rm 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 4.00, 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 200 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?