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An Historical Review of Natural Phenomena and Models That Demonstrates Wave-Particle Duality 1 Reflection and Refraction The Phenomenon Light waves passing through one transparent medium into another are partly reflected and partly transmitted. There is a constant ratio between the angles at which the rays are hitting, reflecting, and passing. 2 Reflection and Refraction The Model Newton, ~ 1650 Light rays consist of particles that obey the laws of classical mechanics. Hugens, ~ 1650 Light rays consist of pinpoint wave sources. The direction of the wave front determines the direction of the ray. 3 Circumvention The Phenomenon Fresnel ~ 1800 Light can “circumvent” obstacles and illuminate regions that should have been shadowed (according to the laws of Geometrical Optics) 4 Interference The Phenomenon Young ~ 1800 Light passing through two slits (d1mm) displays a pattern of alternating dark and light stripes on a screen placed in front of these two slits. 5 Circumvention and Interference The Model 1. Light consists of waves, which are periodic functions 2. The superposition of two waves is also a wave function 3. The light intensity is proportional to the square amplitude of the wave function 6 sin = m / d Diffraction Grating The Model A light ray passing through a ruled slide (d 1µ) splits into a number of rays 7 Diffraction Grating The Model A constructive interference occurs into specific directions. The difference in optical paths for the rays coming from each slit is an integer multiple of the wavelength. d sin = m 8 Electromagnetic Radiation 9 The Phenomenon The Model Hertz 1888 An electric current alternating within a conductor produces a radio-wave propagating at the speed of light Maxwell 1864 Light is an electromagnetic wave The Photoelectric Effect 10 The Phenomenon The Model Mulliken 1916 A surface of metal illuminated by light ejects electrons. The kinetic energy of the electrons is proportional to the frequency of the impinging light. Einstein 1905 Light is composed of particles whose energy is: The Compton Effect The Phenomenon Compton 1923 A laser ray, directed opposite to the flow of a beam of hot sodium atoms, cools the atoms. This occurs due to momentum transfer from the light to the moving atoms. 11 The Model Light is composed of particles with the following momentum: Cathode Radiation The Phenomenon Thomson 1897 Cathode rays are deflected off their pathway by magnetic and electric fields 12 The Model The rays are composed of particles having a negative mass and charge The Oil Drop Experiment The Phenomenon Mulliken 1913 Sprayed oil droplets become electrically charged by an integer multiple of a value ‘e’ charge 13 The Model The charge stems from particles, of which each is charged by the elementary charge ‘e’ The De Broglie Wave The Model De Broglie 1924 Particles can possess a wave-like behavior. The particles’ behavior is analogous to light when it behaves like a particle. 14 The wavelength corresponding to a particle of mass ‘m’ and velocity ‘v’ is: Diffraction of Electrons from a Crystal The Phenomenon Davison-Gremer 1927 When a beam of electrons, accelerated in a low electric field, hits a Ni crystal, it creates a diffraction pattern. 15 Diffraction of Electrons from a Crystal The Model Electrons are waves with a wavelength The three directions of the crystal create three intersecting diffraction patterns 16 Diffraction of Atoms from a Crystal The Phenomenon Stern 1930 A beam of particles (He, H2) hitting a LiF crystal splits into several rays. He 100oK He 300oK 17 20o 15o 10o 5o 0o 5o 10o 15o 20o Atom Diffraction from a Crystal The Phenomenon A supersonic beam of He particles hitting a GaAs crystal splits into numerous rays 18