L12_31Jan_posted - --------------------------------1Physics...

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Unformatted text preview: --------------------------------1Physics 6BThe Second LawofThermodynamics--------------------------------2HousekeepingIf you gave me a DRC form, please confirm via e-mail what youll needfor midterm.Sample Exam (from Spring 2009) + solutions postedReview session for midterm: Sunday 2/6, 7-9pm, Classroom Unit 2Ive removed the limited number of attempts from homeworksWebsite: http://sites.google.com/site/dewey6b/!username: Physics6B!password: *sixB*--------------------------------3Heat and WorkHeatand Workare both forms of energy transferWork(in the physics sense) involves a force acting over a distance!W = !Fds!e.g.,pumping water, moving a car, driving an electric generatorHeatis energy transfer due to atemperature difference!includes almost all forms of energytransfer that arent work--------------------------------4Heat and WorkHumans have used fire for over 100,000 years!only in the last 400 have theyharnessed heat to do work--------------------------------5Looking at a cycleA "C"D"B"AIf this pV diagram represents onemole of amonatomic gas!How net work is done?!How much heat is added?!How much heat leaves incooling?Since we return gas to same state, in cycle as a whole we should see:ABD546KC273K546K1092K0 =!Ucycle= Q W--------------------------------6Looking at a cycleA "C (Constant volume)!W = 0!Q = nCV!T= (1)(1.5R)(273) !3403JC"D (Isobaric)!W = p !V = (2atm)(22.4L) !4538J!Q = n(CV+R)!T= 1(2.5R)(546) !11,343JD "B (Constant volume)!W = 0!Q = nCV!T= (1)(1.5R)(-546) !-6806JB"A (Isobaric)!W = p !V = (1atm)(-22.4L) !-2269J!Q= n(CV+R)!T= (1)(2.5R)(-273) !-5671 JABD546KC273K546K1092Kheating, +workheatingcooling, - workcoolingNet work done:2269 JNet heat input:2269 J--------------------------------7ABD546KC273K546K1092KNet work doneIn a closed cycleon the pV diagramthe area inside the cycle...
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L12_31Jan_posted - --------------------------------1Physics...

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