ism_chapter_20 - Chapter 20 Thermal Properties and...

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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 < 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 σ = where A is the surface area of the body, σ is Stefan’s 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
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