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Atomic and Nuclear Physics Chapters 38-40

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Wave-Particle Duality of Light Youngs Double Slit Experiment (diffraction) proves that light has wave properties So does Interference and Doppler Effect Photoelectric Effect proves that light has properties of particles

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Max Planck From Plancks work on Blackbody Radiation, he proposed that the energy of light is quantized Quantization is an idea that energy comes in bundles or discrete amounts Energy is quantized This idea disagreed with established (traditional) physics

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Photoelectric Effect Light shining on a photo-sensitive metal plate will emit electrons.

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Photoelectric Effect Frequency must be above a minimum (threshold) frequency Brighter light (higher intensity) produces more electrons, but with the same energy Light with higher frequency will emit electrons with higher energy

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Photoelectric Effect

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Law of Conservation of Energy must be followed Energy must be related to frequency Law of Conservation of Momentum must also be followed Light has momentum

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Photoelectric Effect Einstein used Plancks work to explain Photoelectric Effect (Nobel Prize 1921) Proposed that discrete bundles of light energy are photons Energy is proportional to Frequency E=hf h, Plancks Constant 6.63 x 10 -34 J*s

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Photoelectric Effect Conservation of Energy Energy of Photon = Energy of ejected electron + work needed to eject electron (work function, Φ)

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Photoelectric Effect

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Maximum Kinetic Energy is measured by how much voltage (stopping voltage) is needed to stop electron flow KE MAX = qV 1electron stopped by 1 Volt = 1.6 x 10 -19 J 1electron stopped by 1 Volt = 1eV

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Compton Effect 1923 Arthur Compton uses photon model to explain scattering of X-rays Determines equation for momentum of a photon

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Compton Effect X-ray photon strikes an electron at rest After the collision both the electron and X-ray photon recoil (move) in accordance with Laws of Conservation of Momentum and Energy The photon transfers some momentum to the electron during collision.

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Compton Effect Change in wavelength of photon must be related to momentum Magnitude of Photon Momentum:

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de Broglie Wavelength 1923, graduate student, Louis de Broglie suggested that if light waves could exhibit properties of particles, particles of matter should exhibit properties of waves Used same equation as momentum of photon

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Davisson-Germer Experiment Verified de Broglies idea of matter waves Directed beam of electrons at crystal of nickel Electrons showed diffraction pattern Proof that particles have wave properties

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Schrödingers Cat Thought Experiment about basis of quantum mechanics Place cat, vial of poison, Geiger counter with radioactive sample in a seal box. After 1 hour the cat is either alive or dead Cant know without interrupting the experiment (opening the box) The cat is considered BOTH alive and dead

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Atomic Models Daltons Model, early 1800s Hard uniform sphere Plum Pudding Model, 1904 After discovery of electron by J.J. Thomson Rutherford Model, 1909 After Geiger Marsden Experiment

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Atomic Models Bohr Model, 1913 Dense positive nucleus Electrons moving in certain energy levels (orbits)

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Quantum Mechanical Model More detailed view of the Bohr Model Schrödinger Wave Equation and Heisenberg Uncertainty provides region of high probability where electron COULD be. Orbital Modern Model

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Energy Level Transitions Electron energy is quantized Electrons can move between energy levels with gains(absorption) or losses(emission) of specific amounts of energy.

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Energy Level Transitions

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Line Spectra Emission Spectra Shows only the light that is emitted from an electron transition Absorption Spectra Shows a continuous color with certain wavelengths of light missing (absorbed)

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Energy Level Transitions

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Examples: Calculate energy needed for transition from n=1 to n=6 13.22eV Calculate energy released by transition from n=5 to n=2 2.86eV What wavelength of light is this? 434 nm

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Nuclear Physics Nucleus – center of atom Contains nucleons, protons and neutrons Proton, p Positively charged particle, 1e m=1.6726 x 10 -27 kg Neutron, n Neutral particle m=1.6749 x 10 -27 kg

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Atomic Mass Unit Based on Carbon-12 atom 1u = 1.6605 x 10 -27 kg Proton mass = 1.00728 u Neutron mass = 1.00867 u

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Nuclear Reactions Fission and Fusion Energy produced comes from mass being converted into energy (Mass Defect, Δm)

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Mass-Energy Conversion E=mc 2 1 u = 1.4924 x 10 -10 J 1 u = 9.31 x 10 8 eV = 931 MeV

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Fundamental Forces Strong Force Force that holds nucleons (protons and neutrons) together Short range Weak Force Associated with radioactive decay Short Range

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Fundamental Forces Gravitational Force Attractive only Long distance range (think planets) Electromagnetic Force Attractive and repulsive force on charged particles Long range (think stars)

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Classification of Matter Matter is broken down into 2 types Hadrons and Leptons The Quark Family, also called Hadrons, are broken down into 2 types Baryons and Mesons

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Quarks Six quarks Up, Down, Top, Bottom, Strange, and Charm Up, Charm, and Top all have +2/3 charge Down, Strange, and Bottom all have -1/3 charge

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Baryons Baryons are comprised (made of) three quarks The total charge for any baryon is the net charge of the three quarks together Examples: uud = +2/3, +2/3, -1/3 = +1 = proton udd = +2/3, -1/3, -1/3 = 0 = neutron

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Mesons Mesons are comprised of a quark and its antiquark Antimatter Particles that have the same mass but opposite charge of their matter partner Have same symbol as matter but with added bar above symbol Up quark, uup antiquark, ū

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Leptons Leptons are separated into six flavours Electron, Muon, and Tau all have -1 charge Electron neutrino, muon neutrino, and tau neutrino all have 0 charge

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Annihilation When matter and antimatter particles collide, they annihilate each other and produce energy E=mc 2 kg J (use equation) u eV (use conversion on Reference Tables)

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