The device shown in Figure CQ22.7, called a thermoelectric converter, uses a series of semiconductor cells to transform internal energy to electric potential energy, which we will study in Chapter 25. In the photograph on the left, both legs of the device are at the same temperature and no electric potential energy is produced. When one leg is at a higher temperature than the other as shown in the photograph on the right, however, electric potential energy is produced as the device extracts energy from the hot reservoir and drives a small electric motor. (a) Why is the difference in temperature necessary to produce electric potential energy in this demonstration? (b) In what sense does this intriguing experiment demonstrate the second law of
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Chapter 22 Solutions
Physics for Scientists and Engineers, Technology Update (No access codes included)
- A poorly designed electronic device has two bolts attached to different parts of the device that almost touch each other in its interior as shown. The steel and brass bolts are at different electric potentials, and if they touch, a short circuit will develop, damaging the device.The initial gap between the ends of the bolts is d = 5.0 μm at 27°C. At what temperature will the bolts touch? Assume the distance between the walls of the device is not affected by the temperature change.arrow_forwardA bulb delivers 33 W of radiant energy when its filament is at 1900 °C . If the temperature increases by 100 °C , what is the new rate of energy radiated by this bulb? O 39.51 W 36.11 W O 27.56 W O 40.52 Warrow_forwardI often make tea in my microwave oven. I know that it takes two minutes to bring the temperature of a cup of water from room temperature to just about boiling: ready for the teabag. I looked up the characteristics of a microwave oven. Typically their power rating is about 1000 W, but I know that this is the power consumed from the power company, not the power delivered to the water. I looked up the efficiency of microwave ovens, and found that it is about 64%, meaning that a typical oven delivers 640 W to the water. I also looked up the frequency of the microwaves that an oven uses, and found thatf= 2,450 MHz. (a) How much energy is delivered to the water in the making of a cup of tea? (b) What is the wavelength of the microwave? (c) What is the energy of one microwave photon? (d) How many microwave photons are absorbed by the water in making a cup of tea?arrow_forward
- Converting sunlight to electricity with solar cells has an efficiency of ≈15,. It’s possible to achieve a higher efficiency (though currently at higher cost) by using concentrated sunlight as the hot reservoir of a heat engine. Each dish as shown concentrates sunlight on one side of a heat engine, producing a hotreservoir temperature of 650°C. The cold reservoir, ambient air, is approximately 30°C. The actual working efficiency of this device is ≈30,. What is the theoretical maximum efficiency?arrow_forwardConverting sunlight to electricity with solar cells has an efficiency of 15%. It's possible to achieve a higher efficiency (though currently at higher cost) by using concentrated sunlight as the hot reservoir of a heat engine. Each dish in (Figure 1) concentrates sunlight on one side of a heat engine, producing a hot-reservoir temperature of 560 ∘C. The cold reservoir, ambient air, is approximately 30 ∘C. The actual working efficiency of this device is 30%. What is the theoretical maximum efficiency?arrow_forwardUse energy transfers and conservation (energy interaction modelarrow_forward
- 250 students sit in an auditorium listening to a physics lecture. Because they are thinking hard, each is using 125 W of metabolic power, slightly more than they would use at rest. An air conditioner with a COP of 5.0 is being used to keep the room at a constant temperature. What minimum electric powermust be used to operate the air conditioner?arrow_forwardConsider a heat exchanger that has an NTU of 4. Someone proposes to double the size of the heat exchanger and thus double the NTU to 8 in order to increase the effectiveness of the heat exchanger and thus save energy. Would you support this proposal?arrow_forwardThe biggest drawback to extensive use of photovoltaic cells is they produce DC electricity. they don’t work well in cold climates. they are expensive to manufacture. they kill bats and birds. 2. Wind turbines are made to be very tall. This is because they are more stable when they are taller. the wind blows faster higher up. they are quieter the higher up they are. they are safer the higher up they are.arrow_forward
- How much energy does Hannah the Standard Poodle absorb from the sun during a 37-minute walk? Hannah’s fur is matte black, so she absorbs nearly all of the sunlight that hits her; from above, she looks approximately like a rectangle that is 92 cm long and 32 cm wide. The solar intensity in Hannah’s Orange County neighborhood is 1200 W/m2.arrow_forwardA "solar cooker" consists of a curved reflecting mirror that focuses sunlight onto the object to be heated (see the figure below). The solar power per unit area reaching the Earth at the location of a 0.50-m-diameter solar cooker is 600 W/m2. Assuming 50% of the incident energy is converted to thermal energy, how long would it take to boil away 0.9 L of water initially at 33°C? (Neglect the specific heat of the container.)arrow_forwardThe average electricity consumption of a house in Gainesville is known to be 1,007 kWh in a month (One month = 30 days). They would like to install solar panels of 29 % efficiency to generate this electricity. Given that the average solar power density in Gainesville is 5.47 kWh/m2/day, how much surface area must the panels occupy? Calculate the result in m2 but do not write the unit. Round off %3D you answer to a whole number (zero decimal place.)arrow_forward
- Physics for Scientists and Engineers, Technology ...PhysicsISBN:9781305116399Author:Raymond A. Serway, John W. JewettPublisher:Cengage LearningPrinciples of Physics: A Calculus-Based TextPhysicsISBN:9781133104261Author:Raymond A. Serway, John W. JewettPublisher:Cengage Learning