1. Quantum Physics… the world is about to get even weirder!

2. Just when everything seemed to be working… Reading: Moore; Unit Q: chps 1-4 Reading: Moore; Unit Q: chps 1-4 Lord Kelvin’s two small dark clouds: Lord Kelvin’s two small dark clouds: Michelson-Morley Experiment Michelson-Morley Experiment Blackbody radiation Blackbody radiation

3. Planck’s Radiation Law Light (energy) is quantized … E = hf Light (energy) is quantized … E = hf Blackbody spectrum explained! Blackbody spectrum explained!

4. Working with quanta… Energy carried by light… Energy carried by light… E n = nhf E n = nhf Energy quantization of a spring Energy quantization of a spring Wien’s Law and the Stefan-Boltzmann Law Wien’s Law and the Stefan-Boltzmann Law Light does not behave quite like a classical wave! Light does not behave quite like a classical wave! …it gets weirder!

5. The Photoelectric Effect Evidence that light behaves like a particle (sometimes)! Evidence that light behaves like a particle (sometimes)! Enter the photon Enter the photon Concept of the Work Function… Concept of the Work Function… E k = hf - 

6. When waves act like particles! The strange way in which photons interfere with themselves! The strange way in which photons interfere with themselves! Compton Scattering Compton Scattering Light – is it: Light – is it: Wave Wave Particle Particle Both Both Neither? Neither?  

7. When Particles act Like Waves! Prince Louis de Broglie makes a bold prediction Prince Louis de Broglie makes a bold prediction The de Broglie wavelength: The de Broglie wavelength: Confirmed by Davisson and Germer 1927 Confirmed by Davisson and Germer 1927

8. Particles, Waves and Quantons Particle and Wave are macro-world concepts Particle and Wave are macro-world concepts “Quanton” is the quantum world actor “Quanton” is the quantum world actor

9. The Great Heresy! A wave “is a particle” - A particle “is a wave” A wave “is a particle” - A particle “is a wave” The Schroedinger Equation and Heisenberg’s Matrix Mechanics... The Schroedinger Equation and Heisenberg’s Matrix Mechanics......a fundamental blurring of the universe

10. It looks like Heisenberg - I think, I’m pretty sure, I’m not certain... The Uncertainty Principle The Uncertainty Principle

11. The Copenhagen Interpretation... QM is a complete theory that tells us that the world, at the quantum level, is governed by statistical law. It rules out “classical” or “naïve” realist views of nature. As an example, consider the following applet demonstrating the Hydrogen atom. QM is a complete theory that tells us that the world, at the quantum level, is governed by statistical law. It rules out “classical” or “naïve” realist views of nature. As an example, consider the following applet demonstrating the Hydrogen atom.applet demonstrating the Hydrogen atom.applet demonstrating the Hydrogen atom.

12. The Bohr Atom What do you do when theories fail? What do you do when theories fail? Our understanding of atoms and atomic physics circa 1910 Our understanding of atoms and atomic physics circa 1910 currant buns, gold foil, “saturnalia” and others... currant buns, gold foil, “saturnalia” and others... Quantization Quantization the Nicholson atom the Nicholson atom Bohr Bohr applet demonstrating the Hydrogen atom. applet demonstrating the Hydrogen atom.

13. “as soon as I saw Balmer’s formula it all became clear to me” Bohr made two main postulates: Bohr made two main postulates: an atom has a number of stable states in which the electrons orbit the nucleus in accordance with Newton’s Laws but do not radiate energy an atom has a number of stable states in which the electrons orbit the nucleus in accordance with Newton’s Laws but do not radiate energy an atom emits or absorbs energy only when an electron moves from one stable state to another an atom emits or absorbs energy only when an electron moves from one stable state to another

14. Bohr made a further auxilliary assumption electrons moved in orbits for which the orbital angular momentum was quantized... electrons moved in orbits for which the orbital angular momentum was quantized...

15. In Bohr’s footsteps... forces forces energy energy momentum momentum putting it all together... putting it all together...

16. and so.. We can recover Balmer’s formula: We can recover Balmer’s formula:

17. taking stock... We can now: We can now: determine the size of the H atom determine the size of the H atom predict the spectrum of H predict the spectrum of H Can we extend this line of reasoning to other atoms: Can we extend this line of reasoning to other atoms: