PhysicsLAB AP Physics 2
Unit IV - Thermodynamics

  • 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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