chapter 4 survey of astronomy [email protected] astro1010-lee.com
TRANSCRIPT
The Nature or Light and Matter
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
Measuring the Velocity of LightDistance is the measure path from the light source, to the rotating mirror, to the stationary mirror, back to the rotating mirror and to the observer.Time is the time it takes for the spinning mirror turn between reflecting angles.The velocity of light = C = D/T = 500,000 km/sec
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
The Wave Nature of Light
Refraction
Refraction is a property of a wave that causes it to change direction as it passes through a different medium. The longer wavelengths are bent the least, the short are bent the most.
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
The Wave Nature of Light
Diffraction
Diffraction allows the waves to interact with each other, sometimes cancelling and sometime reinforcing.
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
Electromagnetic Wave
The Wave Nature of Light
Visible light is part of an electromagnetic spectrum whose waves travel at the velocity of light. All parts of the spectrum have in common that their waves have both a magnetic and an electric component.
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
Electro-magnetic SpectrumThere is no limit to the lengths of the electro-magnetic waves from the very short gamma waves to the very long radio waves. The various sections of the spectrum have different names but they have many features in common.
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
When solids, liquids or gas at high pressure are heated to incandescence and viewed with at spectrograph the results are Continuous Curves of a characteristic shape. These results are also known as Black Body Curves or Thermal Curves
Thermal Curves
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
Wien’s Law [The hotter the bluer]
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
Stefan-Boltzmann Law [The hotter the brighter]
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
Particle Nature of Light
Definition of a Photon Einstein described the second nature of light as a bundle of energy which was inversely proportional to the wavelength,
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
Non-Thermal Radiation
Spectral lines are images of the entrance slit on the photo plate in each of the colors contained in the original light.
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
Bohr Model of an AtomThe Niels Bohr model of the atom was a major leap forward in our understanding of atomic structure, but it was not the final answer. Bohr postulated that electron orbits about the nucleus are quantized.
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
Non-Thermal Radiation
Hydrogen Absorption Lines
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
Non-Thermal RadiationKirchhoff’s Laws (Schematic)
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
Non-Thermal Radiation
PhotonsProduced and absorbed by electron transitions
TransitionsMovement of electrons between energy levels
Energy levelsStable values of energies for electrons
ExcitationWhen an electron is in any level except the ground stateBy collisions between atoms or by absorption of photons
Light and Matter
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
Doppler EffectOriginal Doppler Experiment
Doppler used friends with ‘perfect pitch’ to make the measurements.
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
Doppler Effect
Doppler Equation
It must be remembered that this equation only measures ‘line of sight’ velocity
Chapter 4Su
rvey o
f A
stro
nom
y
astro1010-lee.com
