Modern%20Physics

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Modern Physics
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Reinventing Gravity

• Einsteins Theory of Special Relativity
• Theorizes the space time fabric.
• Describes why matter interacts.
• The larger the mass the larger the curve in the
  space time fabric.
• Objects that are far away have less interaction

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Duality of Light

• As seen earlier evidence showed that light can be
  refracted by gravity.
• During an eclipse scientists were able to
  photograph EM radiation from stars behind the
  sun.
• The gravity of the sun bent the light.

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Photoelectric Effect(Quantum Theory of Light)

• When EM radiation hits an object and the object
  emits electrons (EX. solar panel)
• The electron receives energy from the EM
  radiation.
• They behaved like particles colliding containing
  a mass and therefore a momentum.
• Einstein called these bundles of energy photons.

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So is light a wave or a particle?

• Both are correct but also both are incomplete.
• Lights dual nature is to this day unexplained in
  full.
• Wave theory - a beam of electrons move as a wave
  also.
• Particle theory - higher intensity should equal
  higher energy electrons
• Actually higher frequency light yields higher
• energy es
• Animation
• E hf or Ehc/?
• E is the energy of the photon
• h is Plancks constant (on PRT)
• f is the frequency of the light

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Sample Problem 1

• Find the energy of a photon of violet light with
  a frequency of 7.69x1014Hz.
• E hf
• E (6.63x10-34Js)(7.69x1014Hz)
• E 5.1x10-19J

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Sample Problem 2

• The wavelength of a certain color of light is
  6.1x10-7m. What is the energy of the photons of
  light?
• Ehc/?
• E ((6.63x10-34Js)(3.00x10 8m/s))/(6.1x10-7m)
• E 3.26x10-19J

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Physics and the Atom

• What happens when light hits an object but does
  not impart enough energy to cause the object to
  emit electrons?
• The Bohr model answers this
• Electrons with the least amount of energy are in
  the ground state.
• If an electron absorbs energy it can transition
  to a higher energy level called an excited state.

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• For an electron to jump energy levels it must
  absorb the exact amount of energy needed.
• The electrons quickly return to ground state and
  a photon is emitted.
• Energy of photon is equal to the energy
  difference between the excited state and the
  ground state.
• Ephoton Ei - Ef
• We will study 2 elements, Mercury and Hydrogen
  (PRTs)
• Energy is given in eV, needs to change to
  J when using Einsteins equations

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Sample Problem

• An electron in an excited hydrogen atom drops
  from the second level to the first energy level.
  Calculate the energy, and the frequency of the
  photon emitted.
• Ephoton Ei - Ef
• E -3.40 - (-13.6)
• E 10.2eV
• (10.2 eV)(1.6x10-19J/eV) 1.62x10-18J
• Ehf
• fE/h
• f 1.62x10-18J/ 6.63x10-34Js
• f 2.4 x1015Hz

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Sample 2

• Is it possible for a Hydrogen atom to absorb
  0.47eV? If so what energy level jump is this
  associated with?
• n4 -gt n6
• -0.38eV - (-.85eV) .47eV

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Subatomic Physics

• Nucleus
• Protons
• Positive charge
• Mass of 1u or 9.31x102MeV
• Neutrons
• Neutral charge
• Mass of 1u
• These are called nucleons

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Binding Energy (mass defect)

• When comparing the mass of nucleus and the sum of
  the particles that make it up, the mass of the
  nucleus is less that the sum of the parts.
• Einstein theorized this missing mass was turned
  into energy used to hold the nucleus together.
• Hence Emc2
• E is energy
• m is mass
• c is the speed of light
• The energy becomes two forces in the atom.

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Binding Energy Forces

• Strong Nuclear Force
• An attractive force that hold nucleons together.
  Or else protons will repel.
• Only effective over very short ranges. 10-15
• Weak Nuclear Force
• The interaction between protons and electrons.
• Appears only during Beta decay as Neutron become
  protons and emit electrons.
• These two plus gravity and electromagnetic forces
  are the 4 known forces of the universe.

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Elementary Particles

• Protons, neutrons and electrons were thought to
  be the smallest particles until 1932.
• The invention of particle accelerators and
  particle detectors have since led to the
  discovery of over 200 new particles.
• They do not exist separately for very long.
• Particle detectors measure how gas and other
  materials interact with these new particles.

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Force Particles

• Theoretical physicists have proposed that the
  forces are an exchange of particles between two
  objects.
• Strong Nuclear Force - gluon particles
• Weak Nuclear Force - WW- Z gauge bosons
• Electromagnetic Force - photon
• Gravity - graviton
• All have been detected except for the graviton

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Classifying Matter

• Open Reference tables to page 3
• All matter is either a hadron or a lepton.
• Leptons do not interact via strong nuclear force,
  hadrons do.
• Leptons
• 6 known - including electrons and neutrinos (no
  charge, less mass than an electron, result of
  nuclear reactions on the sun)
• Hadrons
• Split into Baryons and Mesons both made up of
  quarks.

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Quarks

• 6 quarks that carry a fractional charge.
• Each quark is a different flavor, up, down,
  strange, charm, top, bottom.
• 3 quarks combine to make a baryon such as a
  proton (uud). Composed of 2 up quarks and 1 down.
• By charge 2/3e 2/3e -1/3e 1e
• All baryons must be made of quarks whose charge
  equals a whole number( or - )

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Anti-particles

• For each particle, there is a corresponding
  antiparticle which has an opposite charge but the
  same mass.
• Ex. Positron or anti-electron has the same mass
  as an electron but an opposite charge.
• These particles only exist for short periods of
  time. When they interact with their counterpart,
  they may annihilate releasing photons and gamma
  rays.
• Ex. Cosmic radiation
• Anti-particle or anti-matter has only been found
  in particle accelerators

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Mesons

• Composed of a quark and an anti-quark.
• Less massive than baryons.
• Always have a charge that is a whole number.
• Exist for 10-8 - 10-9 s.

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Grand Unified Theory (GUT)

• The physics on a large scale does not match the
  physics on a quantum scale.
• Theories such as string theory are trying to tie
  the two together in order to create a single
  theory that describes the entire universe.
• Problem string theory requires a minimum of 6
  dimensions of which we only know 4.
  Hypothetically up to 11 dimensions.