AP Physics 2 Unit IV - Thermodynamics

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• 1st Law of Thermodynamics – conservation of energy
• ?U = W + Q
• W = - (area bounded by the PV graph and the x-axis)
• Expansion of a gas is negative work done since the internal energy of the gas is reduced unless heat is added
• Compression of the gas by an external agent is positive work
• Four gas processes – isothermal, adiabatic, isobaric, and isovolumetric LAB – PV measurements of a confined gas
• 1st Law “zero” conditions for isothermal, adiabatic, and isovolumetric
• PV diagrams
• State variables: P, V, U, T, and S (moving from an initial position’s values to a final position’s values)
• Understand when heat will be added or removed during compressions/expansions of each type
• Closed cycles VIDEO DISCUSSION – Discovery of Energy/Heat
• Clockwise cycles define net Work as negative
• VIDEO DISCUSSION – James Watt and the Steam Engine
• U equals zero
• Qnet = -Wnet
• Efficiency formulas eff = W/Qin = 1 – (Qout/Qin)
• Qin = Qout + W
• Carnot Cycle and ideal efficiency
• 2nd Law of Thermodynamics
• If an isolated system undergoes spontaneous change there is an increase in the disorder of the system
• S = Q/T S = k ln(O) Suniverse = 0
• Entropy is a statistical, macro measurement of a system’s disorder – not reversible without doing work on the system
• 3rd Law of Thermodynamics
• Absolute Zero cannot be reached in a finite number of steps (it is a mathematical limit, not an attainable temperature)

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