[an error occurred while processing this directive] Topic Summaries: Modern Physics
 

Topic Summaries: Modern Physics

The Physics Hypertextbook™
© 1998-2008 by Glenn Elert -- A Work in Progress
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  1. Relativity
    1. Space-Time
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    2. Mass-Energy
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    3. General Relativity
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  2. Quantum Physics
    1. Planck's Hypothesis
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    2. Photoelectric Effect
      • Electromagnetic radiation can push electrons free from the surface of a solid.
        • This process is called the photoelectric effect.
        • A material that can exhibit the photoelectric effect is said to be photoemissive.
        • Electrons ejected by the photoelectric effect are called photoelectrons.
      • The photoelectric effect will not occur when the frequency of the incident light is less than the threshold frequency.
        • Different materials have different threshold frequencies.
        • Most elements have threshold frequencies in the ultraviolet region of the electromagnetic spectrum.
      • The maximum kinetic energy of a stream of photoelectrons …
        • is determined by measuring the stopping potential: the applied voltage needed keep the photoelectrons trapped in the photoemissive surface.
        • increases linearly with the frequency of the incident light above the threshold frequency.
        • is independent of the intensity of the incident light.
      • The rate at which photoelectrons are emitted from a photoemissive surface …
        • is determined by measuring the electric current.
        • is directly proportional to the intensity of the incident light when frequency is constant.
      • On a graph of maximum kinetic energy vs. frequency …
        • all curves are linear with slope equal to Planck's Constant.
        • the intercept on the energy-axis is the threshold frequency of the material.
      • Classical physics cannot explain why …
        • no photoelectrons are emitted when the incident light has a frequency below the threshold,
        • the maximum kinetic energy of the photoelectrons increases with the frequency of the incident light,
        • the maximum kinetic energy of the photoelectrons is independent of the intensity of the incident light, and
        • there is essentially no delay between absorption of the radiant energy and the emission of photoelectrons.
      • Modern physics … something, something …
        • photon energy
        • work function
        • more?
      • Equations
        • photoelectric effect

          Kmax = E − ϕ = h(ƒ − ƒ0)

        • photon energy
          E = hƒ =  hc
          λ
        • work function
          ϕ = hƒ0 =  hc
          λ0
        • electron energy

          Kmax = eV0

    3. X-Rays
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    4. Compton Effect
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    5. Antimatter
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    6. Matter Waves
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    7. Uncertainty
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  3. Atomic Physics
    1. Rutherford Model
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    2. Bohr Model
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    3. Schrödinger Model
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  4. Solid State
    1. Band Theory
    2. Semiconductors
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  5. Condensed Matter Physics
    1. Superconductivity
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    2. Superdiamagnetism
    3. Superfluidity
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  6. Nuclear Physics
    1. Isotopes
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    2. Radioactive Decay
      • alpha
      • beta decay processes
        • beta decay
        • positron emission
        • electron capture
        • reverse beta decay
      • gamma
      • neutron
      • proton
    3. Half Life
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    4. Binding Energy
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    5. Fission
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    6. Fusion
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    7. Nucleosynthesis
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    8. Nuclear Weapons
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    9. Radiobiology
      • Radiation is energy in the form of waves and particles that are emitted from a source.
        • It comes in many forms.
        • It is not necessarily a dangerous thing.
      • Visible light divides the electromagnetic spectrum into general regions.
        • infrared and below -- non-ionizing radiation
        • visible light -- able to excite electrons in normal atoms
        • ultraviolet and above -- ionizing radiation
      • The forms of radiation that are especially dangerous to living things are those with energy sufficient to penetrate tissues and then ionize the atoms they pass along the way.
        • They generally have energies on the order of 1 MeV.
        • They damage tissues by disrupting normal cellular chemistry.
        • They are mutagenic (can damage genes) and carcinogenic (can cause cancer).
      • The absorbed dose (D) is the energy absorbed from a source of radiation by some material per kilogram.
        • It only provides a first approximation of the radiobiological damage in a human.
        • The SI unit of absorbed dose is the gray, which is equal to a joule per kilogram [Gy = J/kg].
      • The equivalent dose (H) is the absorbed dose multiplied by the radiation weighting factor (Q) -- a number that varies according to the type of radiation.
        • It relates the absorbed dose to the equivalent radiobiological damage in a human.
        • The SI unit of equivalent dose is the sievert, which is equal to a joule per kilogram [Sv = J/kg].
      • The effective dose (H) is the equivalent dose multiplied by the tissue weighting factor (Q) -- a number that varies according to the organ or tissue exposed.
        • It relates the equivalent dose to the effective radiobiological damage in a human.
        • The SI unit of effective dose is the sievert, which is equal to a joule per kilogram [Sv = J/kg].
      • In symbolic form, the relation between H the equivalent or effective dose, D the absorbed dose, and Q the weighting factor is …
         
        H = QD
         
      • Dose Units Summarized
        • The SI unit of absorbed dose is the gray [Gy].
        • The SI unit of equivalent effective dose is the sievert [Sv].
        • The gray and the sievert are each equal to a joule per kilogram, but they are not equal to each other.
        • The weighting factors are unitless.
  7. Particle Physics
    1. Quantum Electrodynamics
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    2. Quantum Chromodynamics
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    3. Quantum Flavordynamics
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    4. The Standard Model
      • Elementary Particles (pdf) concept map
      • fermions
        • Fermions …
          • are the particles of matter.
          • obey fermi-dirac statistics.
          • have half integral spin (±½ℏ, ±1½ℏ, ±2½ℏ, ±3½ℏ, … ).
          • come in one of twelve flavors.
          • belong to one of three generations.
            1. ordinary matter (the parts needed to make an atom)
            2. exotic matter (produced in high energy collisions)
            3. very exotic matter (produced in high very energy collisions)
        • The elementary fermions are either quarks or leptons.
          • Quarks …
            • come in one of six flavors …
              • three in the up group, each with a charge of +2/3e
                1. up
                2. strange
                3. top
              • three in the down group, each with a charge of −1/3e
                1. down
                2. charm
                3. bottom
            • have a property called color
              • Color is something like electric charge.
              • All quarks can be found in any one of three colors.
                • red
                • green
                • blue
              • Color (in this context) has nothing to do with human vision or visible light.
              • Only quarks and gluons are colored.
            • are more massive than other fermions within the same generation.
            • are always bound to other quarks (by the strong force) at all but exceptionally high energies.
          • Leptons …
            • come in one of six flavors …
              • the three heavy leptons
                  1. electron
                  2. muon
                  3. tauon
                • each with a charge of −e
                • can be found free or bound to other particles (by the electromagnetic force)
                • are less massive than quarks but much, much more massive than the neutrinos
              • and three corresponding neutrinos
                  1. electron neutrino
                  2. muon neutrino
                  3. tauon neutrino
                • all of them are electrically neutral
                • only interact with themselves and other particles via the weak force
                • are very nearly massless
        • The composite fermions arranged in order of increasing complexity are …
          • hadrons: color neutral quark composites
            • mesons: quark-antiquark pairs (pions, etc.)
            • baryons: quark triplets
              • nucleons (protons and neutrons)
              • hyperons (heavy and exotic particles)
          • nuclei: groups of protons and neutrons
          • atoms: nuclei with electrons (one for every proton)
          • molecules: atoms sharing electrons
          • macroscopic material objects: assemblages of atoms and molecules
            (rocks, plants, animals, clouds, planets, stars, etc.)
      • bosons
        • Bosons …
          • are the force particles
          • obey bose-einstein statistics
          • have integral spin (±0ℏ, ±1ℏ, ±2ℏ, ±3ℏ, … )
          • belong to one of four types each associated with a fundamental force
        • Types of Bosons
          • The photon …
            • carries the electromagnetic force between particles with charge
            • has an infinite range
            • is massless
            • exerts a force that is moderately strong relative to the other fundamental forces
            • has no charge or color
            • is described by the theory of quantum electrodynamics (QED)
            • is discussed in more detail in a another section of this book
          • Gluons
            • carry the strong force between particles with color (only quarks and gluons)
            • have a short range (~ 10−15 m, about the diameter of a nucleon)
            • are massless
            • exert a force which is very strong relative to the other fundamental forces
            • come in one of eight color pairs, but carry no charge
            • are described by the theory of quantum chromodynamics (QCD)
            • are discussed in more detail in a another section of this book
          • The intermediate vector bosons
            • carry the weak force between certain particles with flavor
            • have an extremely short range (~ 10−18 m, smaller than any known object)
            • are the only family of bosons with mass
            • exert a force that is moderately weak relative to the other fundamental forces
            • come in charged and uncharged varieties, but are not colored
              • W+ [double u plus] has a charge of +1e
              • W− [double u minus] has a charge of −1e
              • Z0 [zee zero] has no charge
              • Some versions of the standard model include the higgs boson (H+, H−, H0)
            • would be called quantum flavordynamics (QFD), but are usually joined with electromagnetism in electroweak theory (EWT)
            • are discussed in more detail in a another section of this book
          • The graviton …
            • carries the gravitational force between particles with mass-energy
            • has an infinite range
            • is massless
            • extremely weak
            • interacts with all particles including itself (since it possesses energy)
            • would be called quantum geometrodynamics (QGD), but usually called quantum gravitation
            • entirely hypothetical at this point and not a part of the standard model at all
    5. Beyond the Standard Model
      • The unification of physical law [pdf] is an ongoing theme in physics.
        • Historical Unification
          • Newton's theory of universal gravitation unified the …
            • terrestrial gravitation described by Galileo in his laws of falling bodies and projectiles and …
            • celestial gravitation described by Kepler in his three laws of planetary motion.
          • Maxwell's equations of electricity and magnetism (E&M) or electromagnetism unified the theories of …
            • electricity as described by Franklin, Coulomb, et al. with …
            • magnetism as described by Gilbert, Michell, et al. and then subsumed …
            • optics as described by Hooke, Huygens, Newton, Young, et al.
          • In the early Twentieth Century …
            • gravitation was expanded into the theory of general relativity (GR) by Einstein;
            • electromagnetism was expanded into the theory of quantum electrodynamics (QED) by Feynman, Schwinger, Tomanaga, and Dyson; and
            • the strong force was described in the quantum chromodynamics (QCD) of Gell-Mann and Zweig; but
            • the weak force was not described by an independent theory of what is sometimes informally called quantum flavordynamics (QFD).
          • The electroweak theory (EWT) of Glashow, Weinberg, and Salaam extended …
            • quantum electrodynamics, which had been described, to include …
            • quantum flavordynamics, which had not been described.
        • Conjectural Unification
          • By extension, there should probably be a grand unified theory (GUT) that would unite …
            • electroweak theory with …
            • quantum chromodynamics.
          • By extension, there should also be some sort of theory of everything (TOE) that would unite the four fundamental forces of nature …
            • gravity
            • the strong force
            • the weak force
            • electromagnetism
          • The current best cadidate for a theory of everything is some version of string theory.
      • Science is reductionist in nature.
        • Complex entities are built from elementary constituents.
          • Everything is essentially "atomic".
        • The laws describing the behavior of elementary constutents are few in number.
          • All additional "laws" can be dervied from these few laws.

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