Transcript Spectra - MCTCteach

Class Update
• D2L Quiz 5 available; Quiz 6 on Tuesday; Questions on Test 2
• Observations
• Moon Phases
• Due Tuesday, Mar. 3 (2 weeks)
• Friday, Feb. 20
• 8-9:30pm University of Minnesota (Telesc. & Star Gazing [no Moon])
• Sunday, Feb. 22 (Dress Warmly – hat, gloves)
• 7:30-10pm Macalester College (Telescopes, Moon Craters, & Star
Gazing with Raquel)
• Email to reserve your spot in my car if you want a ride to and from
MCTC. Meet at Café Espresso Royale at 6:45pm.
• Macalester Olin Science Building 4th floor, southwest corner
• Street Parking off side streets of Snelling (Osceola & Fairmont)
• No class Thu, Feb. 26 for Student Success Day – Please attend
• Mars and Venus near Moon Friday night (show in Starry Night)
– Venus brighter than Mars
Blackbody Radiation
Atoms and Light
2
3
1
Blackbody Radiation
• Definition:
Spectra
• Radiation emitted by a heated object
•
When not heated, the object is black
•
When heated, the object varies in color depending on
the temperature
• Continuous spectrum
• A black body absorbs and emits radiation
Blackbody Radiation
Examples:
Spectra
• Incandescent light bulb
• Filament changes color as it is heated
• Hot lava
• Sun and other stars
• Heated metal
• Quickly heated ice cube glows
Light Bulb Filament
Solve:
Are there vibrations of the atoms in the filament?
1. Are there many atoms or a few atoms in
the metal filament?
MANY ATOMS
Light Bulb Filament
Solve:
Are there vibrations of the atoms in the filament?
1. MANY ATOMS in the metal filament.
2. True or False: Each atom vibrates at some
frequency.
TRUE
Light Bulb Filament
Solve:
Are there vibrations of the atoms in the filament?
1. MANY ATOMS in the metal filament.
2. Each atom VIBRATES at some frequency.
3. True or False: All atoms vibrate at the same
frequency.
FALSE
Not all vibrate at the same frequency
Many different frequencies
Light Bulb Filament
Solve:
Are there vibrations of the atoms in the filament?
1. MANY ATOMS in the metal filament.
2. Each atom VIBRATES at some frequency.
3. Atoms vibrate at the DIFFERENT frequencies.
Different frequencies correspond to different
wavelengths and display different colors.
Blue light = 400 nm
Red light = 700 nm
Blackbody Radiation
Examples:
Spectra
http://webphysics.davidson.edu/alumni/mi
lee/java/bb_mjl.htm
Side Note:
Intensity = Energy/surface area
Temperature α Energy
Which star is hottest? How do you know?
Which star is hottest? How do you know?
Hotter object has:
More overall radiation (intensity)
Higher peak
Spectrum of the Sun
What do you know from this spectrum?
Absorption – hot dense object with
a gas cloud
Mix of gases (but which ones?)
Spectra
Spectra
Other stars show similar but not
identical line patterns.
So why are there lines in the spectra
at all?
What do those lines mean?
Spectra
of stars
(differences)
Intensity difference
Line differences are
element differences
Annie Cannon
•
•
•
•
Harvard, turn of the last
century
Spectra
Sorted thousands of stars by their patterns of
spectra lines.
Discovered patterns among star spectra
Lines are different for different elements
Hotter
Cooler
UV
λs?, visible?, Temperatures?
Longer λ
Annie
Cannon
Spectra
Hotter
Cooler
O
B
Blue
{
A{
F{
G{
K{
M{
Red
Lines used to categorize wavelength & temperature
Still used today and extended past M for darker red
and brown stars.
Spectra
Spectra
So why are there lines in the spectra at all?
And
What do those lines mean?
Definitions
• Atom
Spectra
– Basic unit of a chemical element
– Has protons, neutrons, & electrons
• Element
– More than 100 substances that cannot
be broken down any simpler
• Molecule
– Group of atoms
http://facstaff.gpc.edu/~pgore/PhysicalScience/atom-with-electrons.gif
Atoms
Spectra
• Protons – positive charge ( + ); larger mass
• Neutrons – neutral, no charge; larger mass
• Electrons – negative charge ( - ); smaller mass
• Nucleus
– protons and neutrons
• Surrounded by
– “orbiting” electrons
http://facstaff.gpc.edu/~pgore/PhysicalScience/atom-with-electrons.gif
Quantum Mechanics
Study of atoms and subatomic particles
Bohr
Model
Ground state Lowest energy level
1. Electrons have certain “orbits” and not others
2. Orbits are closer together as you get further from the nucleus
Quantum Mechanics
Absorb = take in (ex. Increase energy)
Emit = give off (ex. Decrease energy)
When an electron jumps “down”, it emits all the energy at
once in a bundle called a photon (the energy is quantized).
If an electron absorbs a photon of just the right energy, it
jumps “up”.
Of the electron jumps shown, which number of jump
EMITS (gives off) a photon?
2 and 3
Decrease in energy
Of the electron jumps shown, which number of jump
ABSORBS (takes in) a photon?
1
Increase in energy
For the atom shown, a blue and a green photon are emitted
and a red photon is absorbed.
Which jump corresponds to emitting a blue photon?
2
Which jump corresponds to emitting a green photon?
3
Which jump corresponds to absorbing a red photon?
1
Cecilia Payne-Gaposchkin
• Surveyed star spectra
• Discovered stars are about 90% hydrogen
and 10% helium