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PHY 112: Physics II

Chapter 27: Early Quantum Theory and Models of the Atom

Reading Assignment: Giancoli (5th ed) - pages 823 - 851


Be knowledgeable about and capable of working problems in the following areas:

  • Discoveries and Properties of the Electron
  • Planck's Quantum Hypothesis
  • Photon Theory of Light and the Photoelectric Effect
  • Photon Interactions; Compton Effect and Pair Production
  • Wave - Partical Duality; The Principle of Complementarity
  • WAve Nature of Matter
  • Electron Microscopes
  • Early Models of the Atom
  • Atomic Spectra: Key to the Structure of the Atom
  • The Bohr Model
  • de Broglie's Hypothesis Applied to Atoms

    key terms and phrasese/m experiment showed that cathode rays consist of charged particles now known as electrons. As a result of this experiment, the ratio of the charge on an electron (e) to its mass (m) was determined.

    Planck's quantum hypothesis predicts that the molecules in a heated object can vibrate only with discrete amounts of energy. Thus the energy of the vibrating atom is quantized.

    Millikan oil drop experiment determined that the charge on a microscopically small oil drop is always a small whole-number multiple of 1.6 x l0^-19 C. This value equals the charge on the electron. Once the value of the charge on an electron was determined, the accepted value for the mass of the electron was determined to be 9.1 x lO^-31 kg.

    blackbody radiation refers to the intensity of spectral radiation emitted by a "perfectly" radiating object.

    photoelectric effect indicates that light has characteristics of particles. Light particles are called photons.

    threshold frequency is the minimum frequency at which electrons are ejected from a surface.

    work function (Wo) is the minimum energy required to break the electron free from the attractive forces which hold the electron to the surface of a metal.

    pair production occurs when a high energy photon known as a gamma ray traveling near the nucleus of an atom disappears and an electron and a positron may appear in its place.

    positron has the same mass as an electron and carries the same magnitude of electric charge; however, the electron is negatively charged while the positron carries a positive charge.

    wave-particle duality refers to the phenomena where both particles, such as electrons and protons, and light exhibit both the properties of waves and the properties of particles.

    Compton effect shows that the interaction of a photon with an the electron can be viewed as a two-partic1e collision.

    de Broglie wavelength is the wavelength of a particle of mass m traveling at Speed V. The wavelength is given by lambda = h/(mv) where lambda is the wavelength of the particle.

    emission spectra are produced by a high voltage placed across the electrodes of a tube containing a gas under low pressure. The light produced can be separated into its component colors by a diffraction grating. Such analysis reveals a spectrum of discrete lines and not a continuous spectrum.

    Problem Assignment:

    The following problems should be worked to assist you in meeting the Chapter Objectives.
    Problem 1 Page 854
    Problem 5 Page 854
    Problem 15 Page 855
    Problem 27 Page 855
    Problem 49 Page 856

    Tutorial Links

    Physics Tutorial from Prentice Hall

    Peter Jeschofnig, Ph.D., Professor of Science, Colorado Mountain College

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    This page was created by Peter Jeschofnig and was last updated: 1/17/2002