Lecture26

Lecture26 - PHYSICS 149: Lecture 26 Chapter 14: Heat 14.1...

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PHYSICS 149: Lecture 26 • Chapter 14: Heat – 14.1 Internal Energy – 14.2 Heat – 14.3 Heat Capacity and Specific Heat – 14.5 Phase Transitions – 14.6 Thermal Conduction – 14.7 Thermal Convection – 14.8 Thermal Radiation Lecture 26 Purdue University, Physics 149 1
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Final Exam • Thursday, May 5, 3:20 – 5:20 PM • Place: PHYS 333 • Chapters 1 – 15 (only the sections we covered) • The exam is closed book. • The exam is a multiple-choice test. • There will be 30 multiple-choice problems. – Each problem is worth 10 points. • You may make a single crib sheet. – you may write on both sides of an 8.5” × 11.0” sheet. Lecture 10 2 Purdue University, Physics 149
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Internal Energy The internal energy of a system is the total energy of all of the molecules in the system except for the macroscopic kinetic energy (kinetic energy associated with macroscopic translation or rotation) and the external potential energy (energy due to external interactions). Internal energy includes – Translational kinetic energy of the molecules • the average translational kinetic energy of the molecules of an ideal gas < K tr > = (3/2) k T SI (Note: T SI in K) – Rotational and vibrational kinetic energy of the molecules – Potential energy between molecules – Chemical and nuclear binding energy of the molecules Internal energy does not include – any energy related to outside or macroscopic sources or motions, like • overall translational energy of the system • potential energy due to external fields such as gravity. Lecture 26 3 Purdue University, Physics 149
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Energy Conversion: Joule’s Experiment As the two masses fall, they cause paddles to rotate. – Gravitational potential energy is converted into kinetic energy of the paddle wheel. As the paddles agitate the water, it causes water’s temperature rise. – Kinetic energy of the paddle wheel is converted into internal energy. Lecture 26 4 Purdue University, Physics 149
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Lecture 26 Purdue University, Physics 149 5 Heat • Definition: Flow of energy between two objects due to difference in temperature – Note: similar to WORK – Object does not have heat (it has energy) • Units: calorie – Amount of heat needed to raise 1g of water 1ºC – 1 Calorie = 1 kcal = 1000 cal = 4186 Joules • Heat flows from a system at higher temperature to one at lower temperature
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• Objects expand when their temperatures increase because the vibrational energy of their molecules increases; this makes the average distance between molecules increase. – Example: liquid-in-glass thermometer relies on thermal expansion of the mercury or alcohol. Lecture 26
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This note was uploaded on 04/23/2011 for the course PHYS 149 taught by Professor Staff during the Spring '08 term at Purdue.

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Lecture26 - PHYSICS 149: Lecture 26 Chapter 14: Heat 14.1...

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