PHY7A Lecture7

PHY7A Lecture7 - Thermodynamics A thermodynamic system is...

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Thermodynamics A thermodynamic system is one that is made up of very many small interacting pieces . State of a thermodynamic system - The state of a thermodynamic system is determined by macroscopic variables like pressure (P), temperature (T), volume (V), internal energy (U), number of particles (N), and other things like entropy (S) that we will talk about later. These are all called “ state variables ”. If we let our thermodynamic system interact with other systems then the state variables may change. The state our system arrives at when the state variables stop changing is called its “ equilibrium state ”. It is an amazing experimental fact that we can only choose three of these state variables to independently control. Once we have chosen three of them and fixed their values (lets say we choose a certain amount of stuff so we choose N, put it in a specific container so this chooses V, and give it a certain amount of energy so this fixes U) then all the others are fully determined and we can’t change them without changing one of our three fixed variables. Equations of state let us calculate all other state variables from these three.
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PHY7A Lecture7 - Thermodynamics A thermodynamic system is...

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