1. Topic 13 – Waves vs. Particles Mr. Jean
IB Physics 12
Topic 13 – Waves vs. Particles
Mr. Jean

2. The plan: Video clip of the day Millikan’s Spotting experiment
Wave Duality
De Broglie Wave Length
Compton Scattering

10. De Broglie Wavelength

11. Wave - Particle Duality of Light
Modern age physics accepts that light sometimes acts as a wave and at other times acts like a particle.
Both matter and electromagnetic energy exhibit some properties of waves and some properties of particles.

12. Wave Duality: Small Wave Length: Large Wave Length:
Behaves like a particle.
Large Wave Length:
Behaves like a wave.

13. Compton scattering:
This was the second big experiment which proved that photons existed.
It also had some interesting results.

14. With collisions we must consider:
Conservation of Energy:
Conservation of momentum:

16. Compton scattering:
Major discovery supporting Quantum Theory

19. Compton Scattering:
Compton scattering depends on how big the wave is as it interacts with the material’s surface in comparison to the Compton wave length.

20. Compton Scattering http://www.youtube.com/watch?v=fI2C4VlR1OM
This is a list of different videos explaining (some with examples) of the Compton scattering model.

21. The Problem:
Electrons moving around a nucleus in roughly circular or elliptical paths would feel a centripetal force and would therefore have centripetal acceleration.
But accelerating charges produce electric magnetic radiation, therefore these electrons should continuously emit energy, slow down, and eventually collapse into the nucleus.
Obviously, this does not happen.

22. Bohr's Explanation:
Laws of electromagnetism do not apply at atomic level.
Within an atom energy is only absorbed or emitted when electrons change energy levels and this energy is QUANTIZED.
electrons are either in lowest energy state (ground state) or certain allowed levels (excited state).

23. To move from one level to another, electrons must emit or absorb a photon with a certain amount of energy (E = hf).
This absorbed or emitted photon had an energy value equal to the difference between energy levels.

24. Energy Levels:
Bohr found that for the hydrogen atom, the energy associated with a particular level was given by:
En = Energy from change (J)
n = Quantum level

25. Where n is principle quantum number (energy level) and energy is negative because energy is being added to pull the electron away from the nucleus.

27. Changing Energy Levels to Electrons:
This is a great website highlighting states of energy in matter.

28. For the remainder of class:
Review Topics
SL  Review material on Topic #4
HL  Review