Modern Physics Chapters 38-40

Wave-Particle Duality of Light Young’s 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

Max Planck From Planck’s 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

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

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

Photoelectric Effect 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

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

Equations

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

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.

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

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

Standard Model Matter is classified into 2 types Hadrons and Leptons The Quark Family, also called Hadrons, are classified further into 2 types Baryons and Mesons

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

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

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

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

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)

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

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

Mass Defect and Binding Energy Mass Defect Difference between the actual mass of the atom and the sum of the individual masses of the protons, neutrons, and electrons. Binding Energy The amount of energy that must be supplied to a nucleus to completely separate its nuclear particles Mass defect converted to energy, E=mc 2

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