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Reversible and irreversible Processes introduce entropy and the 2 nd law intuitive approach to reversible and irreversible processes later foundation of.

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Presentation on theme: "Reversible and irreversible Processes introduce entropy and the 2 nd law intuitive approach to reversible and irreversible processes later foundation of."— Presentation transcript:

1 Reversible and irreversible Processes introduce entropy and the 2 nd law intuitive approach to reversible and irreversible processes later foundation of thermodynamics Reversible process: can be defined as one whose “direction” can be reversed by an infinitesimal small change in some property of the system. “Gedankenexperiment” to picture a reversible process: Make a video recording of a process 1 2 Run the recording backwards Observable process Process impossible to observe reversible irreversible

2 Examples: Process is possible reversible Backward recording reversible

3 x Small changes can be reversed but gas V 1,T s V 2,T f You never observe reversed process of free expansion reversibleirreversible x

4 TgTg Reversibility is an idealization ( in strictest sense, almost all real processes are irreversible ) Reversibility requires equilibrium processes but Not every equilibrium process is reversible Example > T 0 Q out Almost perfect insulation gas in equilibrium at any time Although system in equilibrium, no small change of the system will reverse the heat flow

5 Dry friction between 2 objects Reversibility is an idealization You never observe the reversed process: object starts to move without assistance

6 x Friction between piston and cylinder irreversibility Heat Conductivity in Solids (an example for irreversibility) Remember: Heat is an energy transferred from one system to another because of temperature difference System  1 System  2 T1T1 > T2T2 Heat Q flows from  1 to  2

7 Heat reservoir  1 Heat reservoir  2 T1T1 > T2T2 L T(x) x T1T1 T2T2 0L * ( in the textbook T 2 >T 1 ) Heat transfer per time interval through homogeneous solid object: where K: thermal conductivity of the rod A: cross-section of the rod A L

8 Electric Systems (examples for reversibility and irreversibility) + - battery #1 : work done against electrical forces per unit charge Work: Current

9 Heat leaving the system Irreversible case RResistor network with total resistance In the steady state: Internal energy of black box unchanged 1. law: Application as heater reversible caseCapacitor network with total CapacityC #1 #2 #1 #2 - Charging an uncharged capacitor - Discharge of the capacitor done by the capacitor No heat transferred(Q=0)


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