Chapter 5: Nature of Light and Matter

  1. How do light and matter interact?
    • emission
    • absorption
    • transmission (transparent objects transmit light, opaque objects block/absorb light)
    • reflection or scattering
  2. Reflection and Scattering
    • mirror reflects light in a particular direction
    • movie screens scatter light in all directions
  3. What is light / Particles of light
    • light can act like a wave or like a particle
    • particles of light are called photons
    • each photon has a wavelength and a frequency
    • the energy of a photon depends on its frequency
  4. Waves
    • a wave is a pattern of motion that can carry energy without carrying matter
    • wavelength: distance between two wave peaks
    • frequency: the number of times per second that a wave vibrates up and down

    • wave speed = wavelength x frequency
    • constant = speed of light = wavelength x frequency
  5. Light
    • electromagnetic waves
    • a light wave is a vibration of electric and magnetic fields
    • light interacts with charged particles through these electric and magnetic fields
  6. Polarization
    • describes the direction in which a light wave is vibrating
    • reflection can change the polarization of light 
    • polarized sunglasses block light that reflects off of horizontal surfaces
  7. Electromagnetic Spectrum
    blue ⇝ red, short ⇝ long: gamma, x ray, UV, infrared, microwaves, radio waves

    the range of wavelengths or frequencies over which electromagnetic radiation extends.
  8. Phases and Pressure
    • phase of a substance depends on both temperature and pressure
    • often more than one phase is present
  9. Emission Line Spectrum
    • a thin or low-density cloud of gas emits light only at specific wavelengths that depend on its composition and temperature, producing a spectrum with bright emission lines 
    • we see bright emission lines at specific wavelengths, but no other light
  10. Continuous Spectrum
    • the spectrum of a common (incandescent) light bulb spans all visible wavelengths, without interruption
    • the spectrum shows a smooth continuous rainbow of light
  11. Absorption Line Spectrum
    • a cloud of gas between us and a light bulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum
    • we see dark absorption lines where the cloud has absorbed lights of specific wavelengths
  12. Chemical Fingerprints
    • each type of atom has a unique set of energy levels and a unique spectral fingerprint
    • each transition corresponds to a unique photon energy, frequency and wavelength
    • downward transitions produce a unique pattern of emission lines
    • because those atoms can absorb photons with those same energies, upward transitions produce a pattern of absorption lines at the same wavelengths
    • observing the fingerprints in a spectrum tells us which kinds of atoms are present
  13. Thermal Radiation
    • an object's thermal radiation spectrum depends solely on temperature
    • nearly all large or dense objects emit thermal radiation including stars, planets, you etc.
    • 1) hotter objects emit more light at all frequencies per unit area
    • 2) hotter objects emit photons with a higher average energy
  14. Doppler Effect
    • the effect that shifts the wavelengths of spectral features in objects that are moving toward or away from the observer 
    • Doppler shift tells us ONLY about the part of an object's motion toward or away from us
    • curved surfaces don't give an echo
  15. Red Shift
    • moving away
    • longer distance between lines
    • emission from bottom
  16. Blue Shift
    • moving toward
    • lines are closer together
    • emission from top
  17. Spectrum of Rotating Objects
    spectral lines are wider when an object rotates faster
  18. Spectroscopy
    in astronomical research it's the process of obtaining spectra from astronomical objects
  19. Quasar
    the brightest type of active galactic nucleus
Card Set
Chapter 5: Nature of Light and Matter
Lecture 5