MidTerm #1 Topics
(incomplete but based on notes, HW, etc)

• E/M Waves
  • Showing if a functional form is a solution to a differential equation and explaining why
  • Using boundary conditions to find constraints on constants in solutions.
  • Wavelength and Frequency are inversely proportional and why
  • Electromagnetic waves are all the same… E and B fields oscillating, light moving in straight line path, all made up of photons.
  • Frequency of charged particle or radio antenna oscillation = frequency of light
  • Electric Fields put forces on charges
  • Electrostatic potential energy due to voltage. KE increase and PE decrease due to change in voltage. Conservation of energy
  • Definition and understanding of eV units
• Photons / Energy/Power:
  • Each photon has certain amount of energy depending on its wavelength.
  • Photon energy can be expressed in J or in eV depending on the situation.
  • Cannot divide a photons energy, all of photon is absorbed at once.
  • Relationship between intensity, energy, photons, and light you see.
  • Power (and frequency) tells you how many photons per second are arriving (and vise versa)
  • # of photons arriving tells you about # of electrons being excited
• Photoelectric effect:
  • Need energy to get out of metal = workfunction
  • Left over energy will be in form of KE of electron
  • KE to PE if negative voltage … can know measure amount of PE if know delta V
  • Not enough photon energy = no current
  • From these ideas calculate workfunction given data, or calculate color of light given data,
  • Current = # of electrons / sec (NOT speed of electrons)
  • Arguments for why a photon view is needed to explain observations.
  • Photoelectric effect observations in real metals:
  • Distribution of electrons in range of energy levels in real metals(no you do not need to memorize work functions for different metals)
  • Incoming photons can hit any of these electrons … not only going to hit most excited
  • Implications for # and KE of electrons ejected and thus, Stopping Potential, current, and shape of I vs V curve.
  • PMT Application of real metal case… (what colors can you detect with a PMT, what is efficiency of detection)
  • Photons have some randomness in time and place in which they are detected, and probability of being detected in a certain spot is related to intensity of light in that spot … connection between wave view and photon view through probability.
  • Observations that support wave view of light and observations that support photon view of light
  • # Photons to energy (J) and power again
  • Again … link between number of photons, intensity, amplitude of E/M wave, color we see (black = no light, no photons)
• Rutherford and idea, reflect at strong angles suggests nature of atomic structure
• Discharge lamps:
  • Insights about electron energy levels in atoms from observations
    Only specific energy levels allowed
    Spacings between energy levels determine color
    Different atoms have different energy levels, with different spacings
    One photon emitted per jump down
    Photons emitted only when electrons jump down in energy
    Color of photon depends only on spacing of energy levels not on absolute value of energy.
    KE of incoming (accelerated) electrons limits maximum of how much atomic electrons can jump up in energy during collision
    Number of free (incoming accelerated ) electrons, determines intensity of light emitted
    if the incoming electrons don't have enough energy to excite the atom, then they pass straight through without interacting (ignoring scattering off the nucleus)
    Conservation of energy:
    Free electron starts with PE
    Gains KE, loses PE as it goes through a voltage difference
    Gives energy to atom causing electron in atom to jump up to higher energy (has more PE here). Any unused KE still in free electron.
    Electron in atom jumps down and loses energy, gives off light energy as photon
    KE of free electron determined by voltage diff, which depends on battery voltage and distance free electron travels.
    Distance free electron travels before hitting an atom determines which levels atom can be excited too and so affects colors emitted.
• Spectra to energy levels and energy levels to spectra
• Spectra to energy levels and energy levels to spectra (yes this is worth studying)
• Idea of ionization energy for electron in atom …
• Lasers:
  • light amplification by stimulated emission of radiation (and what each of these words / concepts means)
  • what a population inversion is
  • how to make a population inversion
  • special characteristics of laser light - (coherence, collimated, pure color)
  • what mirrors do, and exponential growth
  • relating energy, intensity, wavelength, and number of photons
• Interpretation:
  • what model, theory, observation, and inference are
  • the implication of the Farmer and Seeds story on intrepration and scientific reasoning and experiment
• Understand the Bohr model of the Atom, including:
  • Be able to calculate the radial dependence of Potential energy, the effect of the number of protons Z and the energy level n
  • Draw / interpret PE curves
  • What is the total energy depence of the Bohr Model Atom on radius and how does this relate to the ground state energy of -13.6 eV?
  • Calculate associated wavelenghts corresponding to energy level transistions