UH PHYS 1302 - Ch18 (13 pages)

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Ch18



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Ch18

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ch 18 study guide


Pages:
13
School:
University of Houston
Course:
Phys 1302 - Introductory to Physics II

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Chapter 18 The Laws of Thermodynamics 1 The Zeroth Law of Thermodynamics If object A is in thermal equilibrium with object C and object B is separately in thermal equilibrium with object C then objects A and B will be in thermal equilibrium Objects are in thermal equilibrium when they have the same temperature 2 The First Law of Thermodynamics The change in a system s internal energy U Uf Ui is related to the heat Q and the work W as follows U Q W 1 The first law is just conservation of energy specifically including heat Sign conventions Q 0 for heat gained by the system Q 0 for heat lost by the system W 0 for work done by the system W 0 for work done on the system Problem 18 3 A swimmer does 6 7 105 J of work and gives off 4 1 105 J of heat during a workout Determined U W and Q for the swimmer L Whitehead 1 Phys 1302 The work is done by the swimmer so W 6 7 105 J The heat is lost by the swimmer so Q 4 1 105 J U Q W 4 1 105 6 7 105 10 8 105 J The state of a system is determined by the temperature pressure and volume 3 Thermal Processes All of the processes that we re going to talk about are assumed to be quasi static reversible which means they occur so slowly that at any given time the system and its surroundings are in equilibrium We also assume there are no dissipative forces in the system Another way of saying it is that these processes are all reversible For a process to be reversible it must be possible to return both the system and its surroundings to exactly the same states they were in before the process began Friction is an example of an irreversible process Constant Pressure Process Suppose we have gas held in a cylinder with cross sectional area A The pressure is held constant at P0 but the volume of the gas expands moving the piston from position xi to position xf the gas is doing work on the piston The initial volume of the gas is Vi Axi and the final volume of the gas is Vf Axf The force the L Whitehead 2 Phys 1302 gas exerts on the piston is F P0 A



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