Charles Hakes

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Chapter 2

• Spectroscopy /
• Review

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Outline

• Test Wednesday
• Spectroscopy
• Check posted grades!

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Misc

• If you received a C- or below (or any grade you
  have questions about) for your mid-term grade,
  please come by my office to discuss your
  situation.

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Lab notes

• No Inside lab this week
• Constellation presentations soon. This is an
  individual lab.
• Picture
• How to find it
• Interesting objects
• History/Mythology
• Participation

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Lab notes

• Report Lab options. This is a group lab.
• Track the Sunset (Sunrise)
• Track the Moonrise (Moonset)
• Track the motion of (Mars, Jupiter, Saturn)
  against the background stars
• Track the moons of Jupiter (Saturn)
• Track sunspots
• Dark Sky star count
• Other labs that you think up

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Test Topics

• Chapter 0 - review
• Chapter 1 - review, and add
• 1.3 Kepler
• 1.4 Newton
• Chapter 2 - review, and add
• 2.4 Blackbody radiation
• 2.5 Spectroscopy
• Chapter 4 - The Solar System
• 4.1 inventory (review general properties)
• 4.2 debris (asteroids, meteoroids, comets)
• 4.3 solar system formation (nebular theory)

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Test Topics

• Chapter 5 - Earth and Moon
• Entire chapter (particularly atmospheres)
• Chapter 6 - Terrestrial Planets
• 6.3 and 6.8 atmospheres (supplement to 5.3)
• Other sections - just a quick read, on your own.
• Chapter 7 - just a quick read, on your own.
• Review questions on-line

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Photon energy

• The energy of a photon (a packet of light) is
  directly proportional to the frequency of the
  photon.
• High frequency means high energy
• Double the frequency means double the energy of
  the photon.

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Figure 2.10Blackbody Curves

• Note the logarithmic temperature scale.
• For linear scale, go look at the black body
  section of http//solarsystem.colorado.edu/
• example - oven

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Stefans Law

• Total energy radiated (from each m2 of surface
  area) is proportional to the fourth power of the
  temperature (T)4.
• And the Stefan-Boltzmann equation
• F sT4
• (here F is Energy Flux)

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Small Group Exercise

• A pulsating variable star has a temperature
  ranging from 4000 K to 8000 K.
• When it is hottest, each m2 of surface radiates
  how much more energy?
• recall F sT4

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A pulsating variable star has a temperature
ranging from 4000 K to 8000 K.

• When it is hottest, each m2 of surface radiates
  how much more energy?
• A) (sqrt2)x more B) 2x more
• C) 4x more D) 16x more

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A pulsating variable star has a temperature
ranging from 4000 K to 8000 K.

• When it is hottest, each m2 of surface radiates
  how much more energy?
• A) (sqrt2)x more B) 2x more
• C) 4x more D) 16x more

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Group Activity

• You have just baked a cake at 175C, and a Pizza
  at 220C.
• How much more energy is radiated from the Pizza?

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Group Activity

• You have just baked a cake at 175C, and a Pizza
  at 220C.
• How much more energy is radiated from the Pizza?
• convert from C to K

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Group Activity

• You have just baked a cake at 175C, and a Pizza
  at 220C.
• How much more energy is radiated from the Pizza?
• convert from C to K
• use Stefans Law FsT4

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Group Activity

• You have just baked a cake at 175C, and a Pizza
  at 220C.
• How much more energy is radiated from the Pizza?
• convert from C to K
• use Stefans Law FsT4
• compare values using a ratio (pizza/cake)

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How much more energy is radiated by the pizza at
220K than the cake at 175K?

• A) 1.11x more
• B) 1.26x more
• C) 1.47x more
• D) 16x more

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How much more energy is radiated by the pizza at
220K than the cake at 175K?

• A) 1.11x more
• B) 1.26x more
• C) 1.47x more
• D) 16x more

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Spectroscopy
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ROY G BIV
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ROY G BIV

• red
• orange
• yellow
• green
• blue
• indigo
• violet

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Figure 2.11Spectroscope
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Figure 2.12Emission Spectrum
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Figure 2.15Absorption Spectrum
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Figure 2.16Kirchhoffs Laws
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Figure 2.13Elemental Emission
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Figure 2.14Solar Spectrum
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• But where do those lines come from?

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Background

• At the end of the 19th century, many scientists
  believed that they had discovered it all and
  that only details remained to be filled in.
  (Like why are those spectral lines there.)
• Electromagnetic energy appears to come in
  packets, called photons.
• Particle nature of photons helps explain
  interactions with matter.
• Photon energy is directly proportional to
  frequency.

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• Quantum Mechanics
• (How to build an atom)

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How to Build an Atom

• Components
• Proton - heavy, positive charge
• Neutron - heavy, no charge
• Electron - light, negative charge
• Number of protons defines element type (atomic
  number)
• Sum of protons and neutrons defines atomic weight

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How to Build an Atom

• Almost all atom mass is in the nucleus (protons
  and neutrons)
• Protons are held together by nuclear force.
  (Very strong, but very short range.)
• Protons (positive charge) make an
  electromagnetic potential well. (Attracts
  negative charges.)
• Electrons (negative charge) are attracted to the
  well and fill it up until you end up with a
  neutral atom.

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Figure 2.18Modern Atom - note electron cloud
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Some Rules for Atoms

• No two electrons can be in the same state of the
  same atom at the same time.
• Only certain energy levels are allowed.
• Only photons with the same energy as the
  difference between allowed atomic states can be
  absorbed or emitted from an atom.

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Hydrogen Spectrum

• Transitions from excited state to ground state
  will emit ultraviolet light.
• Transitions from higher excited state to first
  excited state emit visible photons.

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Figure 2.19Atomic Excitation
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Figure 2.20Helium and Carbon

• Allowed energy levels are much more complex
  when multiple electrons are involved.
• Allowed energy levels are much more complex
  when multiple nuclei are involved (molecules).

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Figure 2.21Hydrogen Spectra - molecular and
atomic
Atomic spectrum shows the Balmer lines (the H
lines) - Ha, Hb, Hg, etc.
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• Review Questions

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The biggest contributors to global warming are

• A) Water vapor and carbon dioxide
• B) Methane and carbon monoxide
• C) Chlorofluorocarbons (CFCs), which destroy the
  ozone layer
• D) Argon and Helium
• E) Al Gore and Rush Limbaugh

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The biggest contributors to global warming are

• A) Water vapor and carbon dioxide
• B) Methane and carbon monoxide
• C) Chlorofluorocarbons (CFCs), which destroy the
  ozone layer
• D) Argon and Helium
• E) Al Gore and Rush Limbaugh

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Which is correct

• A) wavelength frequency period
• B) wavelength velocity frequency
• C) wavelength / velocity frequency
• D) wavelength / velocity period

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Which is correct

• A) wavelength frequency period
• B) wavelength velocity frequency
• C) wavelength / velocity frequency
• D) wavelength / velocity period

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Which list is in the correct order of
electromagnetic radiation wavelength, going from
shortest to longest?

• A) infrared, ultraviolet, gamma, radio
• B) gamma, x-ray, ultraviolet, visible
• C) radio, infrared, visible, ultraviolet
• D) radio, x-ray, ultraviolet, visible
• E) red, violet, blue, green
•  

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Which list is in the correct order of
electromagnetic radiation wavelength, going from
shortest to longest?

• A) infrared, ultraviolet, gamma, radio
• B) gamma, x-ray, ultraviolet, visible
• C) radio, infrared, visible, ultraviolet
• D) radio, x-ray, ultraviolet, visible
• E) red, violet, blue, green
•  

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Three Minute Paper

• Write 1-3 sentences.
• What was the most important thing you learned
  today?
• What questions do you still have about todays
  topics?