1. Too many particles… can’t keep track! Use pressure (p) and volume (V) instead. Thermal Physics

2. P, V, T Pressure, Volume, Temperature F/A L3L3 Something to do with heat

3. Universe (system + surroundings) System Surroundings Heat Heat is energy in transit Before figuring out what is temperature… What is heat?

4. Heat capacity Specific heat capacity (c) is the heat capacity per unit mass. Empirical relation between temperature and heat

5. Equations of state An equation of state is a mathematical relation between state variables, e.g. p, V & T. This reduces the number of independent variables to two. General form: f (p,V,T) = 0 Example:pV – nRT = 0(ideal gas law) Defines a 2D surface in p-V-T state space. Each point on this surface represents an unique state of the system. f (p,V,T) = 0 Equilibrium state

6. Extensive property:  mass (e.g. V)Extensive property:  mass (e.g. V) Intensive property: not a function of mass (e.g. T, p,  )Intensive property: not a function of mass (e.g. T, p,  ) Specific value:Extensive propertySpecific value:Extensive property Mass Mass State variables Heat is NOT a state variable

7. Ideal gas equation of state Robert Boyle (1627 – 1691) Boyle’s law p  1/V Jacques Charles (1746 – 1823) Charles’ law V  T Joseph Louis Gay-Lussac (1778 - 1850) Gay-Lussac’ law p  T pV = Nk B T k B = 1.38  10 -23 J/K

8. Temperature is what you measure with a thermometer Temperature is the thing that’s the same for two objects, after they’ve been in contact long enough. Long enough so that the two objects are in thermal equilibrium. Time required to reach thermal equilibrium is the relaxation time. What is temperature?

9. Temperature is a measure of the tendency of an object to spontaneously give up/absorb energy to/from its surroundings. Diathermal wall is a boundary that freely allows heat to be exchanged i.e. very short relaxation time for systems separated by a diathermal wall. T 1 - T 2 time T 1 - T 2 time Adiabatic wall

10. AC BC Diathermal wall Zeroth law of thermodynamics If two systems are separately in thermal equilibrium with a third system, they are in thermal equilibrium with each other. C can be considered the thermometer. If C is at a certain temperature then A and B are also at the same temperature.

11. Temperature scales Assign arbitrary numbers to two convenient temperatures such as melting and boiling points of water. 0 and 100 for the celsius scale. Take a certain property of a material and say that it varies linearly with temperature. X = aT + b For a gas thermometer: P = aT + b

12. Platinum resistance thermometer

13. CERNOX thermometer

14. Thermometer needs to have a much lower heat capacity than the sample SampleHeater Thermometer T t T0T0 T 0 +  T T0T0 Relaxation calorimetry

15. What is heat doing at the microscopic level to change the temperature? Heat capacity Specific heat capacity (c) is the heat capacity per unit mass.