Physics Calendar




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Ch 15 Special Relativity - Space and Time - 1

  • Ch 15 & 16 Pretest
  • Ch 15 & 16 Core Ideas, Terms, and Objectives
  • Background - 19th century physics in 15 minutes
    • General state of physics in 1900
    • A few nagging little problems
      • If light is a wave, what does it wave?
        • Why can't we detect the "a luminiferous ether?"
      • Maxwell's "silly" idea
      • Lorentz's "downright crazy" idea
  • Postulates of Special Relativity
    • Laws of physics have the same form in all inertial reference frames
    • Speed of light in a vacuum is constant for all observers (all speeds are not relative)
  • What's so "special" about special relativity?
    • Accelerated versus non-accelerated motion
    • Inertial & Non-inertial reference frames
  • Read:
    • Ch 15
  • Video:
    • "Einstein to the Rescue" (30 min.)
    • "Uncommon Sense - Stretching Time
  • Read Ch 15

Ch 15 Special Relativity - Space and TIme - 2

  • Postulates (review)
    • Laws of physics have the same form in all inertial reference frames
    • Speed of light in a vacuum is constant for all observers (all speeds are not relative)
  • Consequences of Special Relativity
    • Simultaneity
      • The "train thought experiment"
      • Two observers moving at different velocities will not agree on whether 2 events separated in space occur simultaneously, or which one occurs first.
    • Time dilation
      • The "light clock"
        • relative time equation (Lorentz transformation)
      • Why don't we notice time slowing down?
      • At rest, time moves "normally"
      • At "c," time is "frozen"
      • The effect is reciprocal - you see my time running slower
      • Space-time
      • The "Twin Paradox"
      • Relative Velocity
        • relative velocity
      • Does this really work?
        • Ives & Stillwell (1941) - Doppler shift in beams of positive ions
        • Rossi & Hall (1941) - studied the lifetimes of muons produced by cosmic rays in the upper atmosphere
        • Haefle & Keating (1971, 2005) - cesium clock flown around the world compared to stationary clock
        • Confirmed daily in particle accelerator experiments
        • Confirmed by accuracy of the GPS system



Ch 15 Special Relativity - Space and TIme - 3

  • Finish Ch 15
  • Finish yesterday's assignment

Ch 16 Special Relativity - Length, Momentum, & Energy - 1

  • Further consequences of Special Relativity
    • Length contraction
      • L=Lsubo sqrt(1-v^2/c^2)
      • The Barn Problem
    • Momentum, Inertia, and Mass
      • relatistic momentum
    • Energy
      • relativistic energy
      • Eo = mc2
      • Mass is a (very concentrated) form of energy
    • Correspondence Principle
      • Two theories must agree in situations where they overlap.

Ch 16 Special Relativity - Length, Momentum, & Energy - 2

  • Go over the Ch 16 assignment
  • General Theory of Relativity (NOT in the text)
    • Albert Einstein - 1915
    • deals with motion in general (with acceleration)
    • but known as a theory (explanation/model) of gravity
    • Correspondence Principle revisited in a new context
      • equivalence of acceleration and gravitational field
      • the elevator problem (once again!)
    • Some consequences
      • forces are replaced by bending/warping of space time
      • gravity pulls light
      • time slows down where gravity is intense (black holes)
    • Experimental confirmation
      • the eclipse experiment - 1919
      • Haefle & Keating (1971, 2005) - cesium clock flown around the world compared to stationary clock
      • Confirmed by accuracy of the GPS system
  • Finish the assignment from yesterday

Properties of Matter

  • Ch 17 - The Atomic Nature of Matter
    • Matter is made of atoms
    • "Atoms are eternal"
    • Atoms are too small to be seen (approx. 10-10m)
    • Molecules are made of atoms
    • Atoms are made of protons, electrons & neutrons
    • Protons & neutrons reside in the nucleus
    • Nucleus is extremely small compared to atom
    • Almost all of the mass of the atom is in the nucleus
    • Element determined by the number of protons
    • Number of neutrons determine the isotope
    • Electrons "orbit" the nucleus
    • Electron mass is about 1/2000 proton or neutron mass
    • Generally, number of electrons = number of protons
    • Fewer or greater number of electrons determine positive/negative ion.
    • Phases of Matter - solid, liquid, gas, plasma
  • Ch 18 Solids
    • Atoms are more-or-less locked in position
      • Crystals
    • Density
  • Ch 19 Liquids
    • Atoms/molecules are free to slide past one another
  • Ch 20 Gasses
    • Atoms/molecules are free to expand to any volume
  • Plasma
    • "Soup" of free electrons (negative ions) and nuclei (plus inner electrons - positive ions) - outer electrons have too much energy to be held in the atom
      • interiors of stars
    • Excellent conductor of electricity
      • fluorescent lights
    • Most matter is in the plasma state

Unit IV Atomic & Nuclear Physics

Ch 38 The Atom and the Quantum

    • Background
      • Wave terms review
        • Frequency
        • Wavelength
        • Amplitude
      • How do we know that light is a wave (and not made of particles)
        • Standing waves on a spring
          • Constructive interference
          • Destructive interference
        • Interference in 2 dimensions
        • Interference in light means light is a wave
        • Further evidence: the speed of light in water

Review for the quiz

  • Read: Ch. 38

Small Test/Big Quiz on Ch. 15 & 16 - Relativity

Ch 38 The Atom and the Quantum


Ch 38 The Atom and the Quantum

  • The Ultraviolet Catastrophe
    • Theory predicts that hot objects should emit an infinite amount of energy at ultraviolet wavelengths - clearly silly
    • Solution:
      • Max Planck discovered a "fudge factor" in the equations implying that hot objects emit/absorb light in discrete packets called quanta
      • Energy of a quantum depends on frequency: E = hf
      • h is a VERY small constant (6.63 x 1034 J.s)
  • The Photoelectric Effect
    • When light shines on certain metals, electrons are ejected from the metal.
    • Brighter light generally ejects more electrons that dimmer light.
    • Higher frequency light generally ejects faster (more energetic) electrons than lower frequency light.
    • There is a "threshold frequency," which depends on the type of metal, so that light of a lower frequency will not eject any electrons, no matter how bright the light.
    • Einstein's explanation (1905):
      • Light is made of particles, called photons.
      • A photon is a quantum of light, so the energy of a photon depends on its frequency (E = hf).
      • An electron is ejected from the metal when a single photon transfers its energy to a single electron.
      • Brighter light means more photons, so more electrons are ejected by brighter light.
      • Higher frequency light means more energetic photons, so more energetic electrons are ejected by higher frequency light.
      • For light below the threshold frequency, photons do not have enough energy to eject an electron.
  • None (you've suffered enough - for now)

Ch 38 The Atom and the Quantum

  • Particles as waves
    • Louis De Broglie proposed that all particles have wave properties.
      • The wavelength of a particle is inversely proportional to its momentum.
      • The wavelengths of people-sized particles is much too small to be noticed or detected.
      • The wave nature of electrons can be demonstrated
        • Electrons can produce interference patterns.
        • Technology: the electron microscope.
  • Waves as particles
    • Compton Effect (1923) - When an x-ray strikes an electron, the electron recoils as if it had been struck by a particle.


Ch 38 The Atom and the Quantum

  • Video:
    • Lecture 18 - Wave or Particle?
    • Lecture 19 - Quantum Uncertainty - Farewell to Determinism
  • Work on the Ch 38 assignment.

Ch 38 The Atom and the Quantum

  • Models of the Atom
    • Lab Activity - observing line spectra
    • Plum Pudding Model
      • positive charge is spread out with electrons embedded in it
    • Planetary Model
      • a "miniature solar system" with the electric force replacing the gravitational force
      • can't be true, since Maxwell showed that accelerating electric charges emit waves (and therefore lose energy)
    • The Bohr Model
      • electrons don't radiate energy in certain allowed orbits
      • can predict the emission/absorption of specific wavelengths of light by atoms
        • When an electron "jumps" between orbits, the energy difference is emitted/absorbed as a photon of the corresponding frequency (E = hf).
      • Problems:
        • Why don't electrons emit electromagnetic waves in certain orbits?
        • Why these particular orbits (aside from the fact that they can be made to fit the data)?
        • Electrons can't really "jump", since they cannot exist between the allowed orbits - so how do they get there?
          • Electrons disappear from one orbit and immediately appear in another (with the emission/absorption of a photon) without ever being between the two orbits.
    • The De Broglie Model
      • The wave properties of electrons determine the possible orbits of electrons in the atom.
      • An orbit is allowed where the electron wave interferes (with itself) constructively to produce a standing wave.
  • Work on the Ch 38 assignment.

Ch 38 The Atom and the Quantum

  • Quantum mechanics
    • Heisenberg (German)
      • Uncertainty Principle
        • Position/momentum and Energy/time cannot be measured to arbitrary precision
        • The end of the "Clockwork Universe"
        • "Empty" space - The Law of Conservation of Energy/Mass can be violated for a (very) short time.
      • Developed a quantum mechanics based on matrices
    • Schroedinger (Austrian)
      • Developed a quantum mechanics based on waves
        • Equivalent to Heisenberg's matrices, but waves are more familiar to physicists
        • Schroedinger's wave equation (state vector)
          • There is a wave equation that describes the evolution of each property of an object.
          • Square of the amplitude of the wave function is the probability that a measurement will give that value.
    • Bohr and the Copenhagen (Standard) Interpretation of Quantum Mechanics
      • The wave function is a complete description of reality.
      • Collapse of the wave function occurs when a measurement is made.
        • Probability of measured value becomes one, probability of every other possible value becomes zero.
      • Before the measurement, the quantity was in a "superposition of states".
      • Before a property is measured, its value does not exist. (What you can't measure doesn't exist.) The value is created by the measurement.
        • Many people say that quantum mechanics says that "measurement affects the value being measured" but this is a classical - not quantum - idea!
  • Finish the Ch 38 assignment.

Ch 38 The Atom and the Quantum

  • Quantum mechanics (continued)
    • The Schroedinger's Cat Thought Experiment
    • Einstein's objections to quantum mechanics
      • "God does not play dice..."
      • It is silly to say that an object has no definite momentum (for instance) before a measurement is made. It has a value, we just don't know what it is.
        • "Hidden" variables
    • Einstein vs. Bohr (continued)
      • Einstein raises objections to quantum mechanics - twice - Bohr responds - twice - Einstein is embarrassed - twice
      • The Einstein-Podolsky-Rosen Experiment (EPR) - 1935
        • Principle of Locality - One object can't influence what happens to another object unless a signal (traveling at the speed of light) can be sent from one to the other.
        • Principle of Reality - If you can predict the value of a measurement of some quantity before the actual measurement is made, then that quantity must actually exist.
        • Entangled/twin particles
        • The EPR thought experiment
          • Einstein - The universe must be real and local, therefore quantum mechanics cannot be a complete description of it.
          • Bohr - one particle must "influence" the other - what Einstein called (sarcastically) "spooky action at a distance."
        • Bell's Theorem - suggests an actual experiment to decide who's right (1965)
          • The experiment was performed and ______ (its a surprise).
          • Consequences of EPR
    • Alternate interpretations of quantum mechanics
      • The Many-Worlds Interpretation
        • When a measurement is made, the universe "splits" so that every possible value occurs in some universe.
        • popular among string theorists
      • Hidden-Variable Interpretations
        • Bohm and others - very restricted due to the results of EPR
    • Quantum Theory vs. Special Relativity - black holes
      • The theories violate the Correspondence Principle - at least one of them needs some serious work!


  • Finish the Ch 38 assignment.

Last update by JL Stanbrough