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Lecture26 - PHYSICS 220 Lecture 26 Thermodynamics I...

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Lecture 26 Purdue University, Physics 220 1 Lecture 26 Thermodynamics I Textbook Sections: 16.1-16.5 PHYSICS 220
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Lecture 26 Purdue University, Physics 220 2 First Law of Thermodynamics Δ U = Q - W Heat flow into system Increase in internal energy of system Work done by system Equivalent ways of writing 1st Law: Q = Δ U + W The change in internal energy of a system ( Δ U) is equal to the heat flow into the system (Q) minus the work done by the system (W) Energy Conservation
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Lecture 26 Purdue University, Physics 220 3 Signs You are heating some soup in a pan on the stove. To keep it from burning, you also stir the soup. Apply the 1 st law of thermodynamics to the soup. What is the sign of A) Q B) W C) Δ U Positive, heat flows into soup Negative, stirring does work on soup Positive, soup gets warmer
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iClicker Lecture 26 Purdue University, Physics 220 4 A system is acted on by its surroundings in such a way that it receives 50 J of heat while simultaneously doing 20 J of work. What is its net change in internal energy? 1. 70 J 2. 30 J 3. zero 4. -30 J
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Lecture 26 Purdue University, Physics 220 5 W = P Δ V W > 0 if Δ V > 0 expanding system does positive work W < 0 if Δ V < 0 contracting system does negative work W = 0 if Δ V = 0 system with constant volume does no work Work Done by a System M M Δ y W = F d cos θ = P A d = P A Δ y = P Δ V
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Lecture 26
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