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The Laws of Thermodynamics

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Presentation on theme: "The Laws of Thermodynamics"— Presentation transcript:

1 The Laws of Thermodynamics
Zeroth law First law: Energy conservation Third law Second law

2 Other Results from Thermodynamics
Equipartition Degrees of Freedom Stefan-Boltzmann Law Wien’s Displacement Law Phase Diagrams l Tmax = const.

3 Quasi-static processes
Quasi-static processes: near equilibrium States, initial state, final state, intermediate state: p, V & T well defined Sufficiently slow processes = any intermediate state can be considered as at thermal equilibrium. Criterion: It makes sense to define a temperature (ie) there is a statistical average Examples of quasi-static processes: - iso-thermal: T = constant - iso-volumetric: V = constant - iso-baric: P = constant - adiabatic: Q = 0

4 State functions a b c a. isovolumetric b. isobaric a. isobaric
b. isovolumetric isothermal the work done by a system depends on the initial and final states and on the path  it is not a state function. energy transfer by heat also depends on the initial, final, and intermediate states  it is not a state function either.

5 Summary Thermodynamics is just an equilibrium theory.
But natural processes are usually not in eq. and irreversible.  Kinetic theory; statistical mechanics Summary Quasi-static process Character isovolumetric V = constant isobaric P = constant isothermal T = constant adiabatic

6 Blackbody Radiation Spectral energy density of a black body

7

8 Test Plot: Planck formula vs. Wien, Rayleigh

9 Source Wikipedia

10 BBD Theory EM field in a box as superposition of standing waves
Planck: quantize as n* hf Planck Distribution Modes with hf>>kT are exponentially suppressed

11 Summing over modes in 3d for photons The spectrum of the photons

12 Best confirmation: Cosmic Background Radiation
Summing over all frequencies gives the total energy (the Gaussian integral yields pi^4/15) Best confirmation: Cosmic Background Radiation

13 Fitting solar radiation by BBD

14 X-Ray diffraction

15 Bragg’s law:

16 14 Spatial Lattices

17 Visualizing Cubic Lattices

18 Symmetry in Cubic Lattices

19 Hexagonal lattices

20 Miller Indices ~ describing planes
in 3d Lattices

21

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23 Reciprocal Lattice

24 Brillouin Zones and Wigner Seitz cells

25 Reciprocal lattice Diffraction pattern

26 Spectral lines and Symmetry

27 X-Ray Spectra ~ Interpretation

28 Powder Spectra

29 X-rays, practical issues
Rev Sci Instr 3/1939

30 Microwave Radiation, Microwave Horns
J Singal et al. Typical microwave triode design

31 Horn Gain fct of angle Reflection loss horn

32 Theory of EM Horns 1939, reprinted 2006

33 Pyramidal horns, optimal dimensions
Horn antenna types, wikipedia John Kraus ‘Antennas’


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