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Unformatted text preview: Answers to Physics 176 One-Minute Questionnaires Lecture date: February 22, 2011 For the midterm next Thursday, will it cover everything up to HW6? It will include material covered up to and including HW6, as well as all lectures up to and including the March 1 class, and the specific reading that I have been recommending on the Announcements webpage. I would like one example multipart problem working several topics instead of several short examples. (I’m selfish, it helps make my reviewing of notes easier.) Do you mean like Problem 2 in Assignment 5 or Question 4 on Quiz 2? Good problems of those kinds of problems take time to invent, so what you are asking is not a casual request. I do plan to work out a some simple multipart problems in Thursday’s and next Tuesday’s lectures. I also plan to make the 2010 midterm available with answers so you can try to work through those problems and then check your understanding against the solutions. Other than that, there are numerous thermal physics books on reserve and in the library that you can look up for examples of other problems, see http://www.phy.duke.edu/~hsg/176/176-syllabus.html#references What does entropy mean in daily life? How can we apply S = k lnΩ to non-thermal physics concepts? Unless you are a scientist or engineer, I don’t think entropy means much to anyone in daily life. Entropy was invented in the context of practical thermodynamic prob- lems such as designing efficient engines and refrigerators and so is important in almost any context in which one wants to convert energy (often in the form of heat transfer) to some kind of work. Since modern society depends heavily on engines to produce electricity (through spinning steam turbines) and motion (cars, airplanes), entropy is relevant on a daily level. Entropy also plays an important role in understanding biology and in designing communication networks of any kind, so is important also to com- puter scientists, electrical engineers, and neurobiologists. 1 Not sure how to answer your question of how to apply entropy to non- thermal physics concepts, most thermal physics concepts don’t have meaning outside the context in which they were invented, e.g., we have discussed several times that the concepts of entropy and temperature can’t be applied to microscopic systems like a hydrogen atom or electron, you need a system consisting of many elements for thermal physics to apply, and that system further has to be in equilibrium. Most systems on Earth and in the universe are not in equilibrium and so entropy does not give a useful description of their properties. I’ve heard of entropy as a measure of increasing disorder. Who motivated this description?...
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