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Physics Chapter 10

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Tim DeKoninck

on 2 March 2010

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Transcript of Physics Chapter 10

Thermodynamics What to Expect In this chapter, you will learn how two types of energy transfer—work and heat—serve to change a system’s internal energy. You will also learn a new form of the law of energy conservation and will see how machine efficiency is limited. Relationships Between Heat and Work The First Law of Thermodynamics The Second Law of Thermodynamics Heat, Work, and Internal Energy Internal energy can be used to do work Heat and work are energy transferred to or from a system Work done on or by a gas is pressure multiplied by volume change heat and work always refer to energy in transit! An object never has “heat” or “work” in it; it has only internal energy System a set of particles or interacting components considered to be a distinct physical entity for the purpose of study Consider a flask of water A system is rarely completely isolated from its surroundings. Environment the combination of conditions and influences outside a system that affect the behavior of the system work is defined in terms of pressure and volume change Situations: Gas is Compressed Gas Expands Pressure increases but volume does not change? Problems An engine cylinder has a cross-sectional area of 0.010 m^2.How much work can be done by a gas in the cylinder if the gas exerts a constant pressure of 7.5 × 10^5 Pa on the piston and moves the piston a distance of 0.040 m? 1. Gas in a container is at a pressure of 1.6 × 105 Pa and a volume of 4.0 m3. What is the work done by the gas if
a. it expands at constant pressure to twice its initial volume?
b. it is compressed at constant pressure to one-quarter of its initial volume? 2. A gas is enclosed in a container fitted with a piston. The applied pressure is maintained at 599.5 kPa as the piston moves inward, which changes the volume of the gas from 5.317 × 10^−4 m^3 to 2.523 × 10^−4 m^3. How much work is done? Is the work done on or by the gas? Explain your answer. 3. A balloon is inflated with helium at a constant pressure that is 4.3 × 10^5 Pa in excess of atmospheric pressure. If the balloon inflates from a volume of 1.8 × 10^−4 m^3 to 9.5 × 10^−4 m^3, how much work is done on the surrounding air by the helium-filled balloon during this expansion? 4. Steam moves into the cylinder of a steam engine at a constant pressure and does 0.84 J of work on a piston. The diameter of the piston is 1.6 cm, and the piston travels 2.1 cm.What is the pressure of the steam? Physics Chapter 10 Thermodynamic Processes heat (Q) internal energy (U) work (W) energy is transferred as both heat and work one type of energy transfer is dominant other type is negligible real process can be approximated
with an ideal process No work is done in a constant-volume process isovolumetric process a thermodynamic process that