1. Classical ConceptsEquations Newton’s Law Kinetic Energy Momentum Momentum and Energy Speed of light Velocity of a wave Angular Frequency Einstein’s Mass-Energy relation

2. Fifth International Congress of Physics in 1927

3. There are always two contradictory theories about light Theory of Particles Theory of Wave Particle theory explain the fact that light travels in a straight line and reflects on the surface (cannot explain the refraction and diffraction of light) When light is incident on certain metals, the emission of electrons from these metals will be observed Energy of the emitted electrons is independent of the intensity of the light (More intense light → More electrons emitted (not electrons of higher energy) Nature of Light Wave character of light was clearly demonstrated in the reflection, refraction, and diffraction of light Photoelectric Effect Energies of the emitted electrons depend on the frequency of the light

4. Compton demonstrated the particle nature of light (photons) through X-ray scattering When an X-ray photon is scattered by an electron, the frequency of the scattered X-ray photon is less than that of the incident X-ray The scattered photon has less energy (longer wavelength) than the incident photon Duality of Light (Compton Effect) Momentum of photons is also related to the wavelength Energy and Momentum are conserved Light or photons are considered as EM waves that obey Maxwell’s theory Compton Experiment proved that photons not only have energy but also a momentum

5. Compton Effect

6. A moving body behaves in certain ways as if it has a wave nature. Photon Wavelength De Broglie’s Hypothesis

7. De Broglie’s hypothesis could be applied to all matters Interference and Diffraction are wave characteristics (light and X-ray) Electrons as Waves Young’s double-slit experiment with electrons showed interference effect for the electrons showing the wave nature Electrons also showed Interference and Diffraction Electron beam is diffracted by a thin polycrystalline gold film similar to X- ray diffraction predicted by Bragg’s law

8. Heisenberg’s Uncertainty Principle Let us consider a wave group The particle that corresponds to this wave group can be found anywhere within the group at a given time Probability of finding the particle – Maximum in the middle of the group Narrow wave group Particle’s position can be specified more precisely Wavelength of the waves is not well defined (not enough waves to measure λ accurately) Since p = h/λ, particle’s momentum is not a precise quantity If we make a series of momentum measurements, we will find a broad range of values Wide wave group Particle’s wavelength can be specified more precisely Momentum of the particle is a precise quantity Since the wave group is wide, exact position of the particle can not be well defined If we make series of position measurements, we will find a broad range of values Uncertainty Principle It is impossible to know both the exact position and exact momentum of an object at the same time

9. Some Videos http://www.youtube.com/watch?v=9UkkKM1IkKg&feature=related http://www.youtube.com/watch?v=-mNQW5OShMA&feature=related http://www.youtube.com/watch?v=N7BywkIretM&feature=related