1501 Chapter 20 Thermal Properties and Processes Conceptual Problems *1 •Determine the ConceptThe 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)(b3 • Determine the Concept Actually, it can be hard boiled, but it does take quite a bit longer than at sea level. response.best theis)(c4 •Determine the ConceptGases that cannot be liquified by applying pressure at 20°C are those for which Tc< 293 K. These are He, Ar, Ne, H2, O2, NO. *5 •• (a) With increasing altitude, Pdecreases; from curve OF, Tof the liquid-gas interface diminishes, so the boiling temperature decreases. Likewise, from curveOH, 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 ProblemWe 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: 4rATePσ=where Ais the surface area of the body, σis Stefan’s constant, and eis the emissivity of the object. Because Pvaries with the fourth power of T, tripling the temperature increases the rate at which it radiates by a factor of 34and correct.is)(d
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