Charles Hakes
Fort Lewis College
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Chapter 2,9
Stefan’s Law/
Spectroscopy
Charles Hakes
Fort Lewis College
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Outline
• Mid-term grades due - If you receive a
C- or below for your mid-term grade,
please come by my office to discuss
your situation.
• Lab Notes
• Stefan’s Law
• Spectroscopy
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Fort Lewis College
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Lab notes
• Constellation Lab coming up. This is an individual
lab. Read details on-line.
•
•
•
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Picture
How to find it
Interesting objects
History/Mythology
Participation
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Fort Lewis College
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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
• Discuss with lab group and write your option in
folders; list group members
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Fort Lewis College
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Review Questions
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Fort Lewis College
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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
Charles Hakes
Fort Lewis College
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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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Fort Lewis College
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Which is correct
A)
B)
C)
D)
wavelength / velocity = frequency
wavelength / velocity = period
wavelength * frequency = period
wavelength * velocity = frequency
Charles Hakes
Fort Lewis College
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Which is correct
A)
B)
C)
D)
wavelength / velocity = frequency
wavelength / velocity = period
wavelength * frequency = period
wavelength * velocity = frequency
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Fort Lewis College
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Spectroscopy
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Fort Lewis College
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Figure 2.8
Electromagnetic Spectrum
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Fort Lewis College
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ROY G BIV
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Fort Lewis College
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ROY G BIV
•
•
•
•
•
•
•
red
orange
yellow
green
blue
indigo
violet
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Fort Lewis College
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Spectroscopy
• Analysis of radiation that has been
split into component colors…
• Continuous Spectrum
• Emission Spectrum
• Absorption Spectrum
• …and how matter emits and absorbs
that radiation
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Fort Lewis College
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Figure 2.11
Spectroscope
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Fort Lewis College
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Spectroscopy
• Example - Continuous Spectrum
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Fort Lewis College
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Figure 2.12
Emission Spectrum
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Fort Lewis College
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Spectroscopy
• Example - Emission Spectrum
• Each element has a unique “fingerprint”
(Emission Spectrum)
• Plot intensity vs. frequency
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Fort Lewis College
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Figure 2.13
Elemental Emission
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Fort Lewis College
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Spectroscopy
• Example - Emission Spectrum
• Each element has a unique “fingerprint”
(Emission Spectrum)
• Note - Helium
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Fort Lewis College
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Spectroscopy
• Example - Absorption Spectrum
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Fort Lewis College
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Figure 2.15
Absorption Spectrum
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Fort Lewis College
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Figure 2.14
Solar Spectrum
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Fort Lewis College
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Figure 2.16
Kirchhoff’s Laws
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Fort Lewis College
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Kirchhoff’s Laws
•
•
•
A sufficiently dense substance (solid,
liquid, or gas) emits a continuous
spectrum.
A low-density hot gas emits an emission
spectrum.
A low-density cool gas absorbs certain
wavelengths from a continuous spectrum,
leaving an absorption spectrum.
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Fort Lewis College
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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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Fort Lewis College
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Figure 2.9
Ideal Blackbody Curve
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Fort Lewis College
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Stefan’s Law
• Total energy radiated (from each m2
of surface area) is proportional to the
fourth power of the temperature (T)4.
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Fort Lewis College
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Stefan’s 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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Fort Lewis College
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Figure 2.10
Blackbody Curves
•Note the logarithmic
temperature scale.
•For linear scale, go
look at the “black body”
section of:
http://solarsystem.colora
do.edu/
•example - oven
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Fort Lewis College
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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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Fort Lewis College
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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
C) 4x more
Charles Hakes
Fort Lewis College
B) 2x 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
C) 4x more
Charles Hakes
Fort Lewis College
B) 2x 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?
Charles Hakes
Fort Lewis College
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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
Charles Hakes
Fort Lewis College
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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 Stefan’s Law F=sT4
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Fort Lewis College
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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 Stefan’s Law F=sT4
• compare values using a ratio
(pizza/cake)
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Fort Lewis College
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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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Fort Lewis College
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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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Fort Lewis College
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But where do those lines come from?
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Fort Lewis College
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Background
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•
•
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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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Fort Lewis College
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Quantum Mechanics
(How to build an atom)
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Fort Lewis College
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How to Build an Atom
•
Components
•
•
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•
•
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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Fort Lewis College
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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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Fort Lewis College
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Figure 2.18
Modern Atom - note electron “cloud”
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Fort Lewis College
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Some Rules for Atoms
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•
•
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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Fort Lewis College
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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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Fort Lewis College
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Figure 2.19
Atomic Excitation
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Fort Lewis College
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Figure 2.20
Helium 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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Fort Lewis College
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Figure 2.21
Hydrogen Spectra - molecular and atomic
Atomic spectrum shows the Balmer lines
(the “H” lines) - Ha, Hb, Hg, etc.
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Fort Lewis College
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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 today’s topics?
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Fort Lewis College
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