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
Figure CQ22.7
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Physics for Scientists and Engineers With Modern Physics
- 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 thermodynamics?arrow_forwardsometimes the hot water produced by a solar water heater is not warm enough to mee the needs of the occupants of a building. A traditional water heater inside the building supplies additional thermal energy to the solar warmed water. How can this method still reduce the overalll amount of natural gas or electrical energy a building uses?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_forward
- I 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_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 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_forwardA heat engine has a solar collector receiving 600 Btu/h per square foot, inside which a transfer medium is heated to 800 R. The collected energy powers a heat engine that rejects heat at 100 F. If the heat engine should deliver 8500 Btu/h, what is the minimum size (area) of the solar collector?arrow_forward
- At a certain location , the solar power per unit area reaching Earth’s surface is 200 W/m square , average over a 24 hours day. If the average power requirement in your home 4.0 KW you can covert solar power to electric power with 13% efficiency. How large a collector area will you need to meet all your household energy requirements from solar energy?arrow_forwardA hot water heater in a residential home runs for an average of 3.2 hours per day with a heat energy input of 3.7 kW. What would be the annual cost for hot water in this home using a gas hot water heater if the cost of natural gas is $0.33/m3? The gas water heater can get 23 MJ of energy from 1 m3 of natural gas. [round your final answer to zero decimal places]?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_forward
- Use energy transfers and conservation (energy interaction modelarrow_forward250 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_forwardIf you mix food in a blender, the electric motor does work on the system, which consists of the food inside the container. This work can noticeably warm up the food. Suppose the blender motor runs at a power of 250 W for 40 s. During this time, 2000 J of heat flow from the now-warmer food to its cooler surroundings. By how much does the thermal energy of the food increase?arrow_forward
- Principles of Physics: A Calculus-Based TextPhysicsISBN:9781133104261Author:Raymond A. Serway, John W. JewettPublisher:Cengage LearningPhysics for Scientists and Engineers, Technology ...PhysicsISBN:9781305116399Author:Raymond A. Serway, John W. JewettPublisher:Cengage Learning