Thermodynamics Concepts and Laws, Exams of Quantum Physics

Download Thermodynamics Concepts and Laws and more Exams Quantum Physics in PDF only on Docsity! PHYS 1400 Sample Exam Questions: Thermodynamics 1. Distinguish between work and energy. A) Energy is a property: an object may possess energy. Work is a process: an object may do work. B) They are indistinguishable. Both words refer to motion. Any moving object works energetically. C) Work is a property: an object may possess work. Energy is a process: an object performs energy. D) When a gas expands, it has work. When a piston compresses the gas, it has energy. E) Work is a variable, but energy is a constant. An object may do varying amounts of work, but it will always have exactly the same amount of energy. 2. Which of the following is not allowed by the law of energy conservation? A) Energy can be exchanged one form for another; i.e., potential energy can become kinetic. B) Energy can be moved from one object to another as one object does work on the other. C) Energy can be created or destroyed; i.e., as the bowling ball on the carpet slowed down, its kinetic energy was completely destroyed. D) All of the above are allowed and consistent with the law of energy conservation. 3. Which of the following is allowed by the law of energy conservation? A) Energy can be moved from one object to another as one object does work on the other; i.e., as the bowling ball rolled across the carpet, energy was transferred to the carpet in the form of heat. B) Energy can be increased by exchanging one form for another; i.e., as the bowling ball rolled down the ramp, it exchanged potential for kinetic energy, but ended up with more kinetic than potential. C) Energy can be created or destroyed; i.e., as the bowling ball on the carpet slowed down, its kinetic energy was completely destroyed. D) All of the above are allowed and consistent with the law of energy conservation. 4. If an object's internal energy decreases, A) its temperature will also decrease. B) its temperature does not change. C) its temperature will increase. D) its temperature cannot be measured. 5. During the 19th century, why was Lord Kelvin reluctant to accept the idea that the earth must be hundreds of millions of years old? A) Because he did not want to think that the geologists or the biologists were smarter than he was. B) Because he treated the problem as one of thermodynamics, and analyzed the rate of energy loss. His calculations implied a much younger earth. C) Because he perfected a method of dating fossils using radioactive decay, and his fossils were all only a few hundred thousand years old. D) Because he treated the problem as one of trophic levels, and analyzed the ratio of plants to top— level carnivores. Because there were an unusually large number of large carnivores, he concluded that the earth could not be as old as the geologists claimed. 6. Lord Kelvin's method for determining the age of the earth A) is still the standard method accepted today. He was able to determine the earth's age more accurately than anyone has ever been able to do, before or since. B) was modified in the light of new information. He made an assumption (that no energy was being produced from within the earth) that was later shown to be false (when radioactive decay was discovered). C) remained unmodified even after it was shown to be false, because it was only a theory. Scientists have no professional obligation to change their ideas, regardless of whether they are incorrect. 7. The first law of thermodynamics is written: ΔU = Q — W. What does ΔU mean? A) U is the change in external energy created by an object doing work on its surroundings. B) ΔU is the change in an object's internal energy as a result of doing work. C) ΔU is the change in temperature that results when an object's energy increases or decreases. D) ΔU is the change in pressure that results when a piston is used to compress a cylinder of gas. E) ΔU is the change in volume as a result of thermal expansion when temperature increases. 8. According to the first law of thermodynamics, energy A) can be created and destroyed easily and without impact on your system. B) must be constant: the total internal energy of your system remains constant. C) must be conserved: the work done by a system cannot change its internal energy. D) is conserved: it can be moved around as heat or mechanical work, but not created or destroyed. 9. According to the second law of thermodynamics, A) heat will spontaneously flow from a colder body to a warmer body. B) heat engines are always 100% efficient. C) it is possible to construct an operational perpetual motion machine. D) natural processes result in a system’s tendency toward increasing disorder. 10. You set your cup of fresh, hot coffee on the counter while you answer the phone. Ten minutes later, A) the coffee is just as hot as when you left it. Because energy is conserved, the coffee does not change temperature. B) the coffee is much hotter! The coffee has absorbed energy from the counter, and you notice that the countertop is now freezing cold. C) the coffee has cooled considerably. The energy lost by the coffee has been gained by the surroundings: the countertop, the air. D) the coffee has gotten cold because it loses energy. No one knows where the energy goes, it simply disappears from the universe. E) the coffee has cooled because its kinetic energy has been turned into potential energy. No energy has been lost by the coffee, none has been gained by the surroundings. 11. You have a lovely plate of leftover enchiladas from your favorite Mexican restaurant. When you place the leftovers in the refrigerator, they are cooled from room temperature (68°F) to 38°F. A) This is a clear violation of Thermo #2: the plate of food cannot absorb cold from its surroundings, and it is not possible to move energy from the inside of the fridge (cold) to the exterior surroundings (warm). B) This is a violation of Thermo #2, but only because the mass is not conserved. It is not a question of energy at all. C) Thermo #2 is not violated, because this situation is not relevant to any of the laws of thermodynamics. It only becomes an energy problem when you eat the food and digest it. D) Thermo #2 is not violated. The refrigerator is able to chill the plate of food because it draws energy in the form of electricity from an external source. The process is not spontaneous. 12. Why does heat flow from a colder to a warmer object? A) It doesn’t. The warmer object has more energy, and transfers some of it to the colder object that has less energy. B) The warmer object has more energy, but takes even more energy away from the colder object-- this is exactly what happens when you put an ice cube in a glass of warm water. C) The flow of energy is in both directions: from hot to cold and from cold to hot. The energy will transfer back and forth between the objects until they come to the same final equilibrium temperature. 13. What is a heat engine? A) A device that uses work to create heat. B) A device that converts heat energy into useful work. C) A device that moves heat from one object to another without doing any work. D) A theoretical device that has an efficiency of exactly 1. 14. When you ride your bicycle, A) your efficiency is exactly e = 1. This means that all of the energy you input is used to do work (turning the pedals to make the bike move forward). B) your efficiency is e > 1. This is why you ride in the first place, because it is more efficient than walking (and walking has e = 1 because there is a one-to-one ratio between the steps you take and your forward motion). C) your efficiency is e < 1. Not all of the energy you expend is used to do work. Some of the energy ends up going to waste--literally. You will use some of your energy to raise your own temperature.