Physics 121, April 29, 2008. The Second Law of Thermodynamics.Physics 121. April 29, 2008.Slide 3Physics 121. Grade Requirements.Physics 121. Final Exam - Details.Second law of thermodynamics.Second law of thermodynamics. Heat engines.Slide 8Second law of thermodynamics. Heat pumps.Slide 10Slide 11Slide 12Slide 13Second Law of Thermodynamics. The Carnot Cycle.Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Entropy.Slide 24Entropy and the Second Law of Thermodynamics.Physics 121. Do you violate the second law?Physics 121. The End. You are free (and so am I)!Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterPhysics 121, April 29, 2008.The Second Law of Thermodynamics.http://www.horizons.uc.edu/MasterJuly1998/oncampus.htmQuickTime™ and aYUV420 codec decompressorare needed to see this picture.Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterPhysics 121.April 29, 2008.•Course Information•Topics to be discussed today:•The Second Law of Thermodynamics•Applications of the Second Law - the Carnot Engine•Entropy•The End!Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterPhysics 121.April 29, 2008.•Homework set # 10 is now available and is due on Wednesday evening, April 30, at 11.30 pm.•Exam # 3 will be returned in workshops.•Any complaints about Exam # 3 must be addressed by me; please write down why you feel the exam was not graded properly and hand it to me before next Monday, May 5. I will do the re-grading on Tuesday morning, May 6. •I have distributed information about the score you need to obtain on the final exam to get a C-, a B-, and an A- in this course.Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterPhysics 121.Grade Requirements.Physics 121 Final Requirements051015202530-100-90 -80 -70 -60 -50 -40 -30 -20 -10010 20 30 40 50 60 70 80 90100110120130140150160170180190200Required Final Grade (points)Number of StudentsReq. C-Req. A-Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterPhysics 121.Final Exam - Details.•The final exam will be held on Thursday May 8 between 4 pm and 7 pm in Hubbell. The final exam will cover all the material discussed in the course; there will be NO particular focus on thermodynamics. NOTE: no error analysis.•Extra office hours of the TAs and me will be announced via email later this week.•The formula sheet to be attached to the final exam will be distributed via email by the end of the weekend, and will also be available on the WEB.•Please use all the resources at your disposal to prepare for the exam (e.g. the detailed solutions of previous exams, the homework assignments, the study guide, etc.).•The final exam grades will be distributed via email on Monday May 12.Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterSecond law of thermodynamics.•There are several different forms of the second law of thermodynamics:•It is not possible to completely change heat into work with no other change taking place.•Heat flows naturally from a hot object to a cold object; heat will not flow spontaneously from a cold object to a hot object.•Many naturally processes do not violate conservation of energy when executed in reverse, but would violate the second law.Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterSecond law of thermodynamics.Heat engines.•Most engines rely on a temperature difference to operate.•Let’s understand why:•The steam pushes the piston to the right and does work on the piston:Win = nRTin(1-Vin/Vout)•To remove the steam, the piston has to do work on the steam:Wout = nRTout(1-Vout/Vin)•If Tin = Tout: Win + Wout = 0 (no net work is done).•In order to do work Tin > Tout and we must thus cool the steam before compression starts.Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterSecond law of thermodynamics.Heat engines.•The efficiency of an engine is defined as the ratio of the heat extracted from the hot reservoir and the work done:Efficiency = | W | / | QH | •The work done and the heat extracted are usually measured per engine cycle. •Because of the second law, no engine can have a 100% efficiency!•Note: the cost of operation does not only depend on the cost of maintaining the high temperature reservoir, but may also include the cost of maintaining the cold temperature reservoir.Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterSecond law of thermodynamics.Heat pumps.•In many cases (heat engines), the conversion of flow of heat to work is the primary purpose of the engine (e.g. the car engine). •In many other applications (heat pumps), work is converted to a flow of heat (e.g. air conditioning).•The performance of a heat pump is usually specified by providing the coefficient of performance K:K = | QL | / | W |Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterSecond law of thermodynamics.Heat pumps. Note: you can not cool your house by opening the door ofyour refrigerator!Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterSecond law of thermodynamics.Heat pumps.Note: You usually pay for the work done but not for the heat extracted from the outside. You can thus get more energythan what you pay for!Frank L. H. Wolfs Department of Physics and Astronomy, University of RochesterSecond law of thermodynamics.Heat pumps.•Heat pumps:•The heat capacity increases with increasing outside temperature.•Additional heaters may be required in colder climates.•The heat capacity can also be increased by changing the source of heat from the air to the ground.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.http://irc.nrc-cnrc.gc.ca/cbd/cbd195e.htmlQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.http://www.bchydro.com/powersmart/elibrary/elibrary685.htmlFrank L. H. Wolfs Department of Physics and Astronomy, University of RochesterSecond law of thermodynamics.Heat pumps.•Heat pumps:•Heaters in the winter: take heat from the outside to the inside.•Air conditioners in the summer: take heat from the inside to the