Presentation on theme: "First Law of Thermodynamics"— Presentation transcript:
1 First Law of Thermodynamics Work:Total energy transferred to a system by macroscopic forcesexerted on it by other systemsWorkdone by a gas on a pistonAWork done by a fluid as it expandsfrom V0 to VfFluid (gas)F=P AxxEnergy leaves the systemxAEnergy feed in the system
2 Q A First law of thermodynamics: All systems have an internal energy state function that is changedby heat transferred to or from the system and by the workdone by or on the system.nothing but conservation of energyclosed systeminternal energystate functionEnergy transferred bymacroscopic mechanicalmeansEnergy transferred bynon-macroscopic mechanicalmeansAQ
3 Joule’s experiment: the mechanical equivalent of heat What do we learn from the experiment1-dissipative work Wdis done-no heat flow Q-change inmeasuredby change in temperature(V=const.)2-same change incould be created by aheat flow QJoule's Paddle-Wheel Apparatus 1849Change of internal energy U in a dissipative process is the same as ifthere had been a heat flow Q into the system of equal magnitude to Wd.click for virtual experiment
4 Application of 1. law in a free expansion experiment V1 ,TsV2 ,TfThermal insulationgasno heat flow=:adiabatic processfixed wallsno work done by the containerW=01. law:ideal gasU=U(T) for the ideal gas only
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