SM_chapter19 - 19 Temperature CHAPTER OUTLINE 19.2 19.3...

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19 Temperature CHAPTER OUTLINE 19.2 Thermometers and the Celsius Temperature Scale 19.3 The Constant-Volume Gas Thermo- meter and the Absolute Temperature Scale 19.4 Thermal Expansion of Solids and Liquids 19.5 Macroscopic Description of an Ideal Gas ANSWERS TO QUESTIONS Q19.1 The astronaut is referring to the temperature of the lunar surface, speciF cally a 400 °± difference. A thermom- eter would register the temperature of the thermometer liquid. Since there is no atmosphere in the moon, the thermometer will not read the temperature of some other object unless it is placed into the lunar soil. *Q19.2 Answer (e). The thermometer works by differential expansion. As the thermometer is warmed the liquid level falls relative to the tube wall. If the liquid and the tube material were to expand by equal amounts, the thermometer could not be used. Q19.3 Two objects in thermal equilibrium need not be in contact. Consider the two objects that are in thermal equili brium in ±igure 19.1(c). The act of separating them by a small distance does not affect how the molecules are moving inside either object, so they will still be in thermal equilibrium. Q19.4 The copper’s temperature drops and the water temperature rises until both temperatures are the same. Then the metal and the water are in thermal equilibrium. Q19.5 The measurements made with the heated steel tape will be too short—but only by a factor of 51 0 5 × of the measured length. *Q19.6 Mentally multiply 93 m and 17 and 1 / (1 000 000 °C) and say 5 °C for the temperature increase. To simplify, multiply 100 and 100 and 1 / 1 000 000 for an answer in meters: it is on the order of 1 cm, answer (c). *Q19.7 Answer (b). Around atmospheric pressure, 0 °C is the only temperature at which liquid water and solid water can both exist. *Q19.8 Call the process isobaric cooling or isobaric contraction. The rubber wall is easy to stretch. The air inside is nearly at atmospheric pressure originally and stays at atmospheric pressure as the wall moves in, just maintaining equality of pressure outside and inside. The air is nearly an ideal gas to start with, and stays fairly ideal—fairly far from liquefaction—even at 100 K. The water vapor liqueF es and then freezes, and the carbon dioxide turns to snow, but these are minor con- stituents of the air. Thus as the absolute temperature drops to 1 / 3 of its original value the volume (i) will drop to 1 / 3 of what it was: answer (b). (ii) As noted above, the pressure stays nearly constant at 1 atm. Answer (d). *Q19.9 Cylinder A must be at lower pressure. If the gas is thin, PV = nRT applies to both with the same value of nRT for both. Then A will be at one-third the absolute pressure of B. Answer (e). 449
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Q19.10 As the temperature increases, the brass expands. This would effectively increase the distance d from the pivot point to the center of mass of the pendulum, and also increase the moment of inertia of the pendulum. Since the moment of inertia is proportional to d 2 , and the period of a physical pendulum is T I mgd = 2 π , the period would increase, and the clock would run slow.
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This note was uploaded on 01/28/2011 for the course PHYS 011 taught by Professor Nianlin during the Fall '08 term at HKUST.

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SM_chapter19 - 19 Temperature CHAPTER OUTLINE 19.2 19.3...

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