thermal_5_02_08_2011

thermal_5_02_08_2011 - The First Law of Thermodynamics...

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The First Law of Thermodynamics Lecture 5
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First Law of Thermodynamics Overlooks the fine microscopic details (which in many cases are irrelevant). Describes the conversion of one form of energy (heat) into other forms Important Consequences: Conservation of energy Allows estimates of maximum efficiency of energy conversion Completely General! (not just ideal gas) 1 st Law
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The Effect of Heat “Distributed” Energy http://mw2.concord.org/public/part2/heat/page8.cml 1 click
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E int E int = Q + W Statement of 1 st Law (1842) E int represents the distributed energy in a closed system. It can contain contributions from a variety of sources like thermal, chemical, etc. Sign conventionl
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The “system” Universal Appeal! The “system” can be a collection of matter in any form, separated from its surroundings by real or imaginary boundaries. The system may be a biological cell, the contents of a test tube, the gas in a piston, a thin film, or a cup of coffee. How you define a “system” depends on the problem you want to solve.
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If work is done ON a system, it is assigned a positive sign If work is done BY a system (external work or work on the environment), it is assigned a negative sign Sign Conventions When using the 1 st Law, it’s important to determine the proper signs Note: This sign convention is consistent with definition in mechanics in hich work done on a system (eg lifting a box) increases the mechanical Heat (Q) also has a sign associated with it: If system GAINS heat, Q is positive If system LOSES heat, Q is negative An analogy which work done on a system (eg lifting a box) increases the mechanical (potential) energy of the system. By analogy, positive work on a system
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This note was uploaded on 04/23/2011 for the course PHYS 242 taught by Professor Staff during the Spring '08 term at Purdue.

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thermal_5_02_08_2011 - The First Law of Thermodynamics...

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