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Unformatted text preview: 1501 Chapter 20 Thermal Properties and Processes Conceptual Problems *1 Determine the Concept The glass bulb warms and expands first, before the mercury warms and expands. 2 Determine the Concept The heating of the sheet causes the average separation of its molecules to increase. The consequence of this increased separation is that the area of the hole always increases. correct. is ) ( b 3 Determine the Concept Actually, it can be hard boiled, but it does take quite a bit longer than at sea level. response. best the is ) ( c 4 Determine the Concept Gases that cannot be liquified by applying pressure at 20 C are those for which T c &lt; 293 K. These are He, Ar, Ne, H 2 , O 2 , NO. *5 ( a ) With increasing altitude, P decreases; from curve OF, T of the liquid-gas interface diminishes, so the boiling temperature decreases. Likewise, from curve OH, the melting temperature increases with increasing altitude. ( b ) Boiling at a lower temperature means that the cooking time will have to be increased. 6 Picture the Problem We can apply the Stefan-Boltzmann law to relate the rate at which an object radiates thermal energy to its environment. Using the Stefan-Boltzmann law, relate the power radiated by a body to its temperature: 4 r AT e P = where A is the surface area of the body, is Stefans constant, and e is the emissivity of the object. Because P varies with the fourth power of T , tripling the temperature increases the rate at which it radiates by a factor of 3 4 and correct. is ) ( d Chapter 20 1502 *7 Determine the Concept The thermal conductivity of metal and marble is much greater than that of wood; consequently, heat transfer from the hand is more rapid. 8 ( a ) True ( b ) True ( c ) False. The rate at which an object radiates energy is proportional to the fourth power of its absolute temperature. ( d ) False. Water contracts on heating between 0 C and 4 C. ( e ) True 9 Determine the Concept Because atoms are few and far between in space, the earth can not lose heat by conduction or convection. Thermal energy is radiated through space in the form of electromagnetic waves that move at the speed of light. correct. is ) ( c 10 Determine the Concept Because there is little, if any, molecule-to-molecule transportation of energy into a fireplace-heated room, the mechanisms are radiation and convection. 11 Determine the Concept In the absence of matter to support conduction and convection, radiation is the only mechanism. 12 Determine the Concept Because the amount of heat lost by the house is proportional to the difference between the house temperature and that of the outside air, the rate at which the house loses heat (that must be replaced by the furnace) is greater at night when the temperature of the house is kept high than when it is allowed to cool down....
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- Spring '07