L12_31Jan_posted

L12_31Jan_posted - -1Physics 6BThe Second...

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Unformatted text preview: --------------------------------1Physics 6BThe Second LawofThermodynamics--------------------------------2Housekeeping•If you gave me a DRC form, please confirm via e-mail what you’ll needfor midterm.•Sample Exam (from Spring 2009) + solutions posted•Review session for midterm: Sunday 2/6, 7-9pm, Classroom Unit 2•I’ve removed the limited number of attempts from homeworks•Website: http://sites.google.com/site/dewey6b/!username: Physics6B!password: *sixB*--------------------------------3Heat and Work•Heatand Workare both forms of energy transfer•Work(in the physics sense) involves a force acting over a distance…!W = !F·ds!e.g.,pumping water, moving a car, driving an electric generator•Heatis energy transfer due to atemperature difference!includes almost all forms of energytransfer that aren’t work--------------------------------4Heat and Work•Humans have used fire for over 100,000 years!only in the last 400 have theyharnessed heat to do work--------------------------------5Looking at a cycle…•A "C"D"B"A•If 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 cycle…•A "C (Constant volume)!W = 0!Q = nCV!T= (1)(1.5R)(273) !3403J•C"D (Isobaric)!W = p !V = (2atm)(22.4L) !4538J!Q = n(CV+R)!T= 1(2.5R)(546) !11,343J•D "B (Constant volume)!W = 0!Q = nCV!T= (1)(1.5R)(-546) !-6806J•B"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 6BThe Second...

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