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x F =P A First Law of Thermodynamics Work: Total energy transferred to a system by macroscopic forces exerted on it by other systems Work x 0 Fluid (gas)

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Presentation on theme: "x F =P A First Law of Thermodynamics Work: Total energy transferred to a system by macroscopic forces exerted on it by other systems Work x 0 Fluid (gas)"— Presentation transcript:

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2 x F =P A First Law of Thermodynamics Work: Total energy transferred to a system by macroscopic forces exerted on it by other systems Work x 0 Fluid (gas) A done by a gas on a piston Work done by a fluid as it expands from V 0 to V f x A Energy leaves the system Energy feed in the system

3 First law of thermodynamics: All systems have an internal energy state function that is changed by heat transferred to or from the system and by the work done by or on the system. nothing but conservation of energy closed system A internal energy state function Energy transferred by non-macroscopic mechanical means Energy transferred by macroscopic mechanical means Q

4 Joules experiment: the mechanical equivalent of heat Joule's Paddle-Wheel Apparatus Joule's Paddle-Wheel Apparatus 1849 click for virtual experiment What do we learn from the experiment 1 -dissipative work W d is done -no heat flow Q -change in measured by change in temperature (V=const.) 2 -same change in could be created by a heat flow Q Change of internal energy U in a dissipative process is the same as if there had been a heat flow Q into the system of equal magnitude to Wd.

5 Application of 1. law in a free expansion experiment Thermal insulation gas V 1,T s V 2,T f no heat flow =:adiabatic process fixed wallsno work done by the containerW=0 1. law: ideal gas U=U(T) for the ideal gas only


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