MASTERING PHYSICS PHY132 HW 17-2

MASTERING PHYSICS PHY132 HW 17-2 - HW17.2 Due: 11:00pm on...

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HW17.2 Due: 11:00pm on Wednesday, October 20, 2010 Note: To understand how points are awarded, read your instructor's Grading Policy . [ Switch to Standard Assignment View] Specific Heat, Latent Heat, and Temperature versus Time Graphs Learning Goal: To understand specific heat and latent heat and how they are related to temperature versus time graphs. Energy can be added to a system either by doing work on it or by adding heat to it. Energy transfer by work requires a force to act through some distance. Energy transfer in the form of heat occurs between objects that are at different temperatures, with energy spontaneously traveling from the higher-temperature object to the lower-temperature one. When energy is added to an isolated system in the form of heat, either the temperature of the system will increase or the system will undergo a phase change at a fixed temperature. The specific heat of a sample characterizes the rate at which it changes temperature per unit mass when it receives energy in the form of heat. The relationship between the energy input in the form of heat and the resulting temperature change is , where is the mass of the sample and is its specific heat, which depends on its phase. For this problem, assume that specific heat values are a constant for all temperatures within a given phase, which is a good approximation. The latent heat of a sample characterizes how much energy is required per unit mass to force the system to undergo a phase change at a fixed temperature. The amount of energy input in the form of heat required to completely change the phase of a sample with mass is . Phase changes between solid and liquid phases are characterized by a latent heat of fusion . Phase changes between liquid and gas phases are characterized by a latent heat of vaporization . In general, every phase (solid, liquid, or gas) has its own specific heat value and every phase change has its own latent heat value. This graph in the figure shows how the temperature of an initially solid sample changes as time goes by when it is placed above a flame that delivers a constant heating power (that is, a fixed amount of energy input in the form of heat each second). The process occurs in five distinct steps: Increase the temperature of the solid until it reaches its melting temperature. Melt the solid to form a liquid, maintaining a constant temperature. Increase the temperature of the liquid until it reaches its boiling temperature. Boil away all the liquid to form a gas, maintaining a constant temperature. Increase the temperature of the gas (this assumes that the gaseous sample is confined). [ Print ]
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Part A Use the graph to rank the sizes of the following: specific heat of the solid, specific heat of the liquid, specific heat of the gas, Keep in mind that energy is being delivered to the system in the form of heat at a constant rate by the flame. Hint A.1
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MASTERING PHYSICS PHY132 HW 17-2 - HW17.2 Due: 11:00pm on...

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