Transcript Slide 1

Big Bang, Black
Holes, No Math
ASTR/PHYS 109
Dr. David Toback
Lecture 10, 11 & 12
Physics We Need
Big Bang, Black
Holes, No Math Topic 3: Quantum Mechanics and Atoms
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Was Due for Today – L10
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions:
– Let us know if you have been misgraded
– Unit 1 Revision: New grades posted soon.
– Unit 2 Revision (if desired): Stage 2
• End-of-Chapter Quizzes:
– Chapter 6
• Paper 1:
– Stage 1 due Monday before class
– Can submit a draft for feedback on eCampus if
you like
– MUST submit to Physics
turnitin
on eCampus
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Big Bang, Black
Holes, No Math Topic 3: Quantum Mechanics and Atoms
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Was Due for Today – L11
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions:
– Let us know if you have been misgraded
– Unit 1 Revision: Grades posted soon (still doing
regrades)
– Unit 2 Revision (if desired): Stage 2
• End-of-Chapter Quizzes:
– Chapter 6
• Paper 1:
– Stage 1 due Monday before class
– MUST submit to turnitin on eCampus
• Honors Paper:
Physics We Need
Big Bang, Black
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–
Stage
0
due
today
Holes, No Math Topic 3: Quantum Mechanics and Atoms
Was Due for Today – L12
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions:
– Let us know if you have been misgraded
– Unit 1 Revision: Grades posted
• Email sent about how to pass if you haven’t
passed already
• End-of-Chapter Quizzes:
– Chapter 6
• Paper 1:
– Stage 1 in CPR and turnitin on eCampus
• Honors Paper:
– Stage 1 due March 11th
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Heads Up: Paper 1
• What is the
evidence for
Dark Matter?
• This will be
the topic of
Paper 1
• In order to
understand the
evidence, we
next talk about
Dark Matter
• Will be due 1
week after we
finish Chapter 6
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Papers in CPR/Schedule
Schedule is Like PLRQ since it is in CPR:
Each Paper has 4 (or 6) Steps:
1. Mentioned after we start the chapter (just did that)
2. Assigned after we finish the chapter
3. Submit text 1 week later (Stage 1)
4. Calibrations/Reviews/Self-Assessment due the week
after that (Stage 2)
5. Revision (optional): Stage 1 due one week later
6. If you did a Stage 1, Calibrations/Reviews/SelfAssessment due one week after that
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Style of the Paper
• Explain it to someone who isn’t taking
the class (no jargon)
• ~600 words (This is the equivalent of
both side of a sheet of paper, double
spaced)
• No citations! Use your own words
• Text should be professional. You are
“trusted guide” not a “buddy” or
“comedian”
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Paper Format
• Must follow expected Format
• Usually 5 paragraphs. Needs:
– Introduction paragraph
– 1 paragraph per piece of evidence (3
total?)
– Conclusion paragraph that ties it
together
– http://faculty.physics.tamu.edu/tobac
k/109/WritingAssignments/samplepaper
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Holes, No Math Topic 3: Quantum Mechanics and Atoms
Help Available for Stage I
• Submit a draft for feedback from the
TA
– Submit on eCampus in “Rough Drafts
(Optional)”
– Drafts due Friday at midnight
– If you submit late, we can try to give
feedback but we can’t guarantee it
• We also recommend going to the writing
center
Physics We Need
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Biggest reason people don’t do well
1. Read ALL the instructions on CPR
– See the FAQ on papers
2. Don’t forget to submit to
turnitin.com
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Best Guess Schedule
•Paper
•Paper
•Paper
•Paper
1:
2:
3:
4:
Text
Text
Text
Text
due
due
due
due
10/1 (Ch 6)
10/15 (Ch 8)
11/1 (Ch 12)
11/15 (Ch 17)
•Honors Stage 0 (not in CPR): Due
10/6
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So Far
Topics
1.Light and Doppler Shifts  Done
2.Gravity, General Relativity and
Dark Matter Done
3.Atomic Physics and Quantum
Mechanics  Now
4.Nuclear Physics and Chemistry
5.Temperature and Thermal
Equilibrium
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Where We Are Going Next
In Chapter 3 we learned a little
about how the stuff of the
Universe is put together
• Big things are made from
LOTS of small things
• Small things: The Fundamental
Building Blocks of Nature
–What is the “stuff” in
atoms?
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The Largest Stuff
• Most of the light we see
from space comes from stars
• What are stars made of?
– Stars are lots of atoms
interacting
– The ways they interact
creates light we can see
– Can study the distant
stars by looking at the
light from them
– Can study atoms here on
Earth. Are they
the
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same?
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How do Atoms work?
• ElectroMagnetism (electric charge)
– What holds electrons and protons
together
• Quantum Mechanics
– The funny way atoms form
– Electrons in orbits
– Atoms absorbing and emitting
photons (light)
Chapter 7
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Different Types of Atoms
Chapter 8
• The Strong Force
– Keeps protons and neutrons together
in the atomic nucleus
– Different types of nuclei
 different types of atoms
– Different atoms  Different light…
• Nuclear Physics and Chemistry
• Studying the Stars using their light
– Spectral lines of the atoms
– Atomic “fingerprints”
– The light we see from the stars
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Overview of the story
• Big things are made from LOTS of small things
• Small things: The Fundamental Building Blocks of Nature
– What is the “stuff” in atoms
• ElectroMagnetism (electric charge)
– What holds electrons and protons together
• Quantum Mechanics
– Why atoms form the way they do
– Electron in orbits
– Atoms absorbing and emitting photons (light)
This
Lecture
• The Strong Force
– Keeps protons and neutrons together
Next
– Different types of nuclei  different types of atoms
Lecture
– Different atoms  Different light…
• Nuclear Physics and Chemistry Different TYPES of Atoms
• Studying the Stars using their light
– Spectral lines of the atoms
– Atomic “fingerprints”
– The Black
light we see from Physics
the stars
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The Fundamental Building Blocks
Our best understanding:
The very BIG stuff is
made up of LOTS of
very small stuff
Need to understand:
1. What are the
fundamental building
blocks of nature
2. How it’s all held
together
3. How they “create” the
light we see
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Early evidence for the Atomic Model
Shoot atoms at a “target”
Theory:
Experiment
(1910’s):
1?
Bag stuffed with cotton
2?
Bag stuffed with cotton and a few
small rocks
The experiment gives
results like #2!
The positive charge in an atom and most of its mass is
concentrated in a tiny, very dense center: The Nucleus
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The Building Blocks of Nature
In the 19-teens
and 20’s
experiments
determined:
• Atoms are made
of a nucleus
surrounded by
electrons
– Many types of
nuclei
–
Only
one
kind
of
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Math Topic 3: Quantum Mechanics and Atoms
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Nuclear Physics
Many years later (using many
of the same methods):
• Nucleus is composed of
neutrons and protons
• Number of protons and
neutrons in the nucleus
determines the atom type
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The Fundamental Building Blocks of Nature
• Electrons
Talked about this
• Neutrons
in Chapter 3
More in Chapter 8
• Protons
– Neutrons and Protons are
really made of quarks
•Discovered in the 1970’s
•We’ll talk more about this in
the next chapter
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Putting Them Together
How do we put these
fundamental building
blocks together to
form atoms?
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Overview of the story
• Big things are made from LOTS of small things
• Small things: The Fundamental Building Blocks of Nature
– What is the “stuff” in atoms
• ElectroMagnetism (electric charge)
– What holds electrons and protons together
• Quantum Mechanics
– Why atoms form the way they do
– Electron in orbits
– Atoms absorbing and emitting photons (light)
• The Strong Force
– Keeping protons and neutrons together
– Different kinds of nuclei
• Nuclear Physics and Chemistry  different atoms
• Spectral lines of the atoms
– Atomic “fingerprints”
– The light we see from the stars
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This
Lecture
Next
Lecture
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ElectroMagnetism
• You probably already
know that protons and
electrons have
“electric” charges
• Positive charge and
negative charge attract
each other
• Call this
ElectroMagnetism
+
-
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Weirdness…
You probably never
thought about it
this way but in
many ways the
way things with
electric charge
attract is the
same as in gravity
+
-
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Gravity vs. ElectroMagnetism
Gravity
• Every object in the
universe attracts
every other object in
the universe
• The bigger the mass,
the bigger the
attraction
• The further the
distance between the
objects, the smaller
the attraction
ElectroMagnetism
• Every charged object
in the universe
“attracts” every other
charged object in the
universe
• The bigger the charge,
the bigger the
attraction
• The further the
distance between the
objects, the smaller
the attraction
Physics 202
Physics 201
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Physics
208
Physics
218
3: Quantum Mechanics and Atoms
Holes, No
Math Topic
What’s different?
•Gravity:
– All objects attract no matter what
– (As far as we know…)
•ElectroMagnetism:
– Ignores neutral particles
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Other Differences
•ElectroMagnetism is MUCH
stronger than gravity
•If I have two electrons, the
electric force between them is
so powerful that it is 1042 times
stronger than gravity
–Can “ignore” gravity inside
atoms
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Aside
• ElectroMagnetism is MUCH
weaker than the Strong Force
• For two quarks inside a proton
the Strong Force is ~100
times stronger than the EM
force
– Can almost “ignore” EM
inside protons
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Atomic Physics
How do we make up atoms?
1.Start with a simple (partially
wrong) atomic model
– Positive Nucleus attracts the
negatively charged electrons
and keeps them in “orbit”
2.Then move to the weird world
of Quantum Mechanics
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A Hydrogen Atom
The simplest
atom:
Figure not
to scale
-
Hydrogen
One electron
and one
proton
(Partially wrong)
|
+
|
~10-15 m
|
~10-10 m
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|
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Is the world this simple?
• This is a nice simple model
• Why does the electron
stay in “orbit”?
• Simple (partially wrong)
answer: There is a
“Force” that keeps it in
orbit just like Gravity
keeps the Earth orbiting
the Sun
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Problem
• ElectroMagnitism says electrons slow
down when they move in circles
• Observe this for electrons moving in
big circles
• Should be true for electrons in small
circles (atoms) also
 Spiral down until they hit the
nucleus and we’d have nothing: No
atoms!
–Would take ~10 picoseconds (10-11s)
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Another Problem
• Stars can be in orbit any distance
from the center of the galaxy
– Depends only on their speed
• Electrons should, depending on
their speed, be able to be almost
anywhere near the nucleus (like a
planet or a comet)
• Don’t observe this… Only specific
distances from the nucleus
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Overview of the story
• Big things are made from LOTS of small things
• Small things: The Fundamental Building Blocks of Nature
– What is the “stuff” in atoms
• ElectroMagnetism (electric charge)
– What holds electrons and protons together
• Quantum Mechanics
– Why atoms form the way they do
– Electron in orbits
– Atoms absorbing and emitting photons (light)
• Different TYPES of Atoms
– The Strong Force
– Keeping protons and neutrons together (atomic nuclei)
– Nuclear Physics and Chemistry
– Different atoms  Different light…
• Studying the Stars using their light
– Spectral lines of the atoms
– Atomic “fingerprints”
– The light we see from the stars
Physics We Need
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This
Lecture
Next
Lecture
36
Quantum Mechanics
• How do we explain these weird
features that we observe about
Atoms?
• Quantum Mechanics!
• LOTS we COULD say about QM,
but since we could spend years on
this we’ll focus only on the most
important points you need
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Quantum Mechanics
Two big issues:
1. All particles can be described both as
particles AND waves
– Saw this for photons
– True for electrons (and protons etc.) also!
2. In atoms: Electrons can ONLY be in one of
the available energy states, and at certain
distances from the nucleus
– Keep atoms from collapsing! (Good!)
– “Quantizes” the interactions with light i.e.
only some energy photons interact with
atoms
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Energy of Electron Waves
• Small energy
electron have
large
wavelengths
• Small
wavelength
electrons have
large
energy
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Only Orbits with Specific Wavelengths Work
• The electron “wave”
has to go all the way
around
• Can have one
peak/trough, two
peaks/troughs, three
peaks/troughts etc…
– A quantized number
– The Quantum in
Quantum Mechanics
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Only Orbits with Specific Wavelengths Work
• Lower Energy
and closer to the
nucleus
• Higher Energy
and further away
from the nucleus
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Energy and Distance from The Nucleus
Higher
Energy and
further away
from the
nucleus
Lower
Energy and
closer to
the nucleus
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Only these levels
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are
allowed!
Topic 3: Quantum Mechanics and
Atoms
How Photons Interact with an Atom
• To understand better how photons
interact with the stuff in an atom,
“how we’ll SEE atoms”, we need to
say a bit more about Energy and
about Quantum Mechanics
• Lots of different ways they can
interact… start with the simple
interactions
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Simple: Photon-Atom Collision
• Before: Start with a high energy photon and
a low energy atom
• After: Lower energy photon, higher energy
atom (like two billiard balls colliding)
• Same TOTAL energy before and after
collision
– Conservation of Energy
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Clicker Question
After a collision with a
stationary atom, the energy
of a photon is
a) Higher
b) Lower
c) Same
Physics We Need
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Clicker Question
After a collision with a
stationary atom, the speed
of a photon is
a) Higher
b) Lower
c) Same
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Clicker Question
After a collision with a
stationary atom, the
wavelength of a photon is
a) Longer
b) Shorter
c) Same
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Atom-Photon Perspective
• Photon’s perspective: I
collide with a low energy
atom and “transfer” some of
my energy
• Atom’s perspective: I collide
with a high energy photon
and “take” some of its
energy
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Quantum Mechanics and EM
• In General Relativity we found that it is
better to describe the “force” of gravity as
the curvature of space-time
• How do we “better” describe
ElectroMagnetism, especially with Quantum
Mechanics?
– Electric fields
• Answer: In ElectroMagnetism “Force” is
essentially all about the “emission” and
“absorption” of photons by charged particles
like electrons and protons
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Quantum Mechanics – Force Carriers
• Think of the force between
electrically charged things
as being caused by the
exchange of “virtual”
photons
• The force, or interaction, is
“carried” by particles
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Example with Two Electrons
• First electron emits a “force-carrying”
particle (a photon)
• Causes a recoil of the first electron
– You shoot a gun and lurch back
• The other electron “catches” it and gets
“banged”
– Your friend gets hit with the bullet
and falls backward
• Net result: The two particles move
differently, “as if” there were a force
between them
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Visualizing Our Analogy
1: Two electrons hanging out
2: electron on the right “emits” a
photon and “recoils”
-
-
3: Photon bangs into the left electron
and bumps it
Both now move apart: Same sign
charges “repel” each other
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A Proton and Electron
1: A proton and an electron hanging out
2: Proton on the right “emits” a
photon and “recoils”
-
+
3: Photon bangs into the electron
Doesn’t transfer Momentum
Transfers information on how to move
Opposite signs attract
For those of you who know a little bit, this
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is
how
“electric
fields”
work
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More Interactions
• Can also get electrons and protons
interacting with REAL photons
– Photons we can see, as opposed
to ones that are emitted then
absorbed never to be seen
outside the interaction
• Real photons can be emitted or
absorbed
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Electron and Photon Interacting
Electron can “absorb” a photon
 Electron becomes more energetic
-
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Electron Emitting a Photon
Electron can “emit” a photon
 Electron becomes less
energetic
-
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A Simple way of drawing things:
Feynman Diagrams
Electron can “absorb”
a photon  becomes
more energetic
Electron can “emit” a
photon  becomes
less energetic
e
e
e
e
g
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g
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Feynman Diagram for an Atom
Hydrogen Atom
P
P
g
e-
e-
• A diagram of
how the
particles
“talk” to each
other
• These two
are attracted
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Photon and Atom
If a photon with
the right energy
hits an atom
and is absorbed,
the electron can
“jump” to an
“excited state”
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Excited Atom Emits a Photon
If an atom is in
an excited
state, it’s just a
matter of time
before it emits
a photon with
exactly the
energy between
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two
states
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Other ways of drawing the same
thing
• An electron can move into a
more energetic orbit when it
absorbs a real photon with
exactly the right energy
• The photon is absorbed,
and the electron goes into
an excited state
• A high energy atom can
“emit” a photon and go into a
lower energy state
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A Proton bumps into an atom
and excites it
Atom in a
Higher Energy
State
Atom in
Lowest Energy
State
Proton
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An Excited Atom Emits a Photon
Atom in
Lowest State
Atom in a high
Energy State
Photon with
a specific
energy
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Absorbing and Emitting a Photon
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http://bigbang.physics.tamu.edu/Figures/StolenAnimations/bohr.swf
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Lots of Different Energy States
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http://bigbang.physics.tamu.edu/Figures/StolenAnimations/BohrAtom.avi
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Photons and Atoms
Photons can interact with Atoms in three ways
1.Very low energy photon: Because the electron
in the atoms can only have quantized states
around the nucleus VERY low energy photons
will be ignored, or bump the path of the atom
– Ignoring is a kind of interaction
2.If an atom encounters a photon with the
“right energy” photon it can get “excited” and
go into a higher energy state. Photon is
absorbed and is gone forever
3.If a REALLY energetic photon comes along it
can completely knock an electron out of orbit
from a nucleus
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Putting it All Together
A cartoon of an atom and a photon
Note: The electron being completely out of the
atom is a perfectly good “energy state”
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Atomic Transitions
•Any photon that hits the atom with
the right energy will be absorbed
•Absorbs only special colors
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How is this helpful?
• Can look at light
from a light bulb
 all colors
observed
• Look at light from
a light bulb with
Hydrogen gas in
the way
– Only special
Atomic Fingerprinting
colors will be
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absorbed!
Holes, No Math Topic 3: Quantum Mechanics and Atoms
Outline for Unit 2: Physics We Need
1. Light and Doppler Shifts Done
2. Gravity, General Relativity and
Dark Matter Done
3. Atomic Physics and Quantum
Mechanics Done
4. Nuclear Physics and Chemistry 
Next
5. Temperature and Thermal
Equilibrium
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Prep For Next Time – L10
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions:
– Let us know if you have been misgraded
– Unit 1 Revision: New grades posted soon.
– Unit 2 Revision (if desired): Stage 2
• End-of-Chapter Quizzes:
– If we finished Chapter 7 then End-of-Chapter Quiz 7a &
7b (else, just through Chapter 6)
• Paper 1:
– Stage 1 due Monday before class
– Can submit a draft for feedback on eCampus if you like by
FRIDAY
– MUST submit to turnitin on eCampus
Physics We Need
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Prep For Next Time – L11
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions:
– Let us know if you have been misgraded
– Will post Unit 1 Revision grades soon
• End-of-Chapter Quizzes:
– If we finished Chapter 7 then End-of-Chapter Quiz 7a &
7b (else, just through Chapter 6)
• Paper 1:
– Stage 1 due Monday before class
– MUST submit to turnitin on eCampus
• Honors Paper:
– Stage 0 due today
– Stage 1 due March 11
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Full set of Readings So Far
•Required:
– BBBHNM: Chap 1-8
•Recommended:
– BHOT: Chap. 1-6, 9 and 11
(117-122)
– SHU: Chap. 1-3, 6 and 7 (upto page 153)
– TOE: Chap. 1
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Clicker Question
What would happen to the Einstein
ring around a galaxy who's Dark
Matter suddenly wasn't there?
a)
b)
c)
d)
e)
Nothing
It would get smaller
It would get bigger
It would disappear
None of the above
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Clicker Question
What would happen if you were shot by a gun
that fires "dark matter” bullets which have
the same size and mass as a regular bullet?
a) Your molecules would significantly spread
out from an expansion of space-time
b) A black hole would form inside you
c) Objects behind you would be gravitationally
lensed
d) Your body would barely notice
e) You would die like you would if you got shot
with any kind of Physics
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Clicker Question
Why is dark matter "dark“?
a) Because it is closely linked to
dark energy
b) Because it has no mass
c) Because it is made of black
holes
d) Because it doesn’t interact
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Clicker Question
As far as we know, Dark Matter
exists:
a) Everywhere in the universe
b) Only near black holes
c) Mostly in or around galaxies
d) It doesn't exist
e) We don't know where it
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exists
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Clicker Question
A man shoots a red photon straight up
into the air next to a very tall
building. The photon rises in the air.
Which statements are true:
a) The photon slows down as it rises,
the same way a rock would
b) The photon loses energy, the same
way a rock would
c) The photon gets blue-shifted
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Clicker Question
Instead of throwing a rock into the air, a man shoots a red photon straight up
into the air next to a very tall building. The following question are about the
photon when it reaches the top of the building. Which of the following
statements are true
Question 1: Speed
a) The speed of the photon stays the same
b) The speed of the photon slows down like a rock would
Question 2: Energy
a) The energy of the photon stays the same
b) The energy of the photon gets lower (like the kinetic energy would for a rock)
c) The energy of the photon gets larger (since it is getting closer to outer space)
Question 3: Color
a) The color of the photon stays the same
b) The color of the photon is red-shifted (gets a longer wavelength)
c) The color of the photon is blue-shifted (gets a shorter wavelength)
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Clicker Question
A hydrogen atom is hit by a photon and the electron
absorbs the photon and moves to an excited state.
Later, a photon with the exact same energy is emitted
from the atom, and the electron moves back to its
original state.
Is this the same photon as before?
a) Yes, it was inside the electron
b) Yes, it was bouncing around inside the atom
c) No, the electron destroyed the original photon and
created the new photon
d) No, the nucleus destroyed the original photon and
created the new photon
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Paper 1 Stuff
• Paper 1 is Pass/Fail
– Grade now posted on eLearning
• May change as we do re-grades
– Reasons you might have failed:
• Overall grade was low
• Calibrations were low
• Self-assessment was low
• Didn’t turn in on time
– Need an extension? Tell me IN ADVANCE
– Will assess late penalties for late papers
• You need a passing grade to pass the course
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Paper 1 Stuff Continued
• Check if you are grading fairly:
– Count the number of no’s in your Rubric. 5 no’s? Can’t be a
“great paper” and receive a 9.
• Were you misgraded?
– Send us an email ASAP and we’ll look
• Need to revise to get a passing grade?
– CPR Revision now open
– Same procedure, but grading will emphasize your paper
– Text due Monday before class
– Calibration the following Monday
– Need help? Send us an email
• Paper 2: due 1 week after we finish Chapter 8
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More Quantum Weirdness
Electron can “absorb”
a photon  becomes
more energetic
g
e
e
e
Electron can “emit” a
photon  becomes
less energetic
g
e
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Prep For Next Time – L9
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions:
– Let us know if you have been misgraded
– Unit 1 Revision: New grades posted soon.
– Unit 2 Revision (if desired): Stage 2
• End-of-Chapter Quizzes:
– Chapter 6
• Paper 1:
– Stage 1 due Monday before class
– Can submit a draft for feedback on eCampus if
you like
– MUST submit to Physics
turnitin
on eCampus
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Summary: Atoms vs. Planets
Quantum Mechanical effects
only the very small (atoms)
• Electron orbits around a
nucleus: Quantized “radii”
• Planets around the Sun: Not
Quantized (too big)
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• Aside: Actually true for the Earth
also. However, it would take 1024 years
(a Quadrillion years, or a yotta-year)
to spiral down into the Sun. That’s a
billion times the lifetime of the
universe
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Atomic Transitions
• What happens if a
photon doesn’t have
the exact right energy
to excite an atom it
meets?
• Passes the atom
unabsorbed
• Note… knocking the
electron completely
out of the atom is
a perfectly good
“excited state”
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Wrong energy
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Special Photon Energies
Atoms only “absorb”
or “emit” Special
wavelength photons
• Can only go from
one state to
another
–Only specific
colors absorbed
–Only photons with
specific energy
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Analogy
Think about Asteroids (or other
space junk) banging into the Earth
• Small piece of junk: Not much
happens
• Big asteroid: Wipes out the
dinosaurs
• REALLY BIG Asteroid: Knocks the
Earth out of orbit and off into
space (this would be bad)
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Aside
Smaller:
• As far as we know all protons (and
neutrons) are identical
• Each particle has an anti-particle
– More on this stuff later
Bigger:
• How atoms combine to form molecules
and how molecules interact is really
chemistry
– Won’t spend too much time on this
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Other Questions
• What are stars made of?
• What can we learn from looking
at them?
• How do we know?
Need to know about the stuff
out there and how it interacts
to create the light we see on
Earth
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Big Picture: Looking at the Heavens
What we know about
the universe comes
from multiple places
• Already earned
about the light
coming from the
heavens
• Need to know more
about WHAT
PRODUCES the light
we observe
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Only Orbits with Specific Wavelengths Work
• The electron
“wave” has to go
all the way around
• Can “wave” once,
twice, three times
etc…
– A quantized
number
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Only Orbits with Specific Wavelengths Work
• Lower Energy
and closer to the
nucleus
• Higher Energy
and further away
from the nucleus
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Paper Stuff
• Paper 1 now in progress
– The calibration and review
portions are due by Wed Feb
24th, BEFORE class
• Paper 2 will be due 1 week
after we finish Chapter 8
– Tentatively, due March 8th
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What Do we Need to Know?
When we look at the
heavens, we want
an answer to the
question “what IS
all that stuff
made of?”
Going Further: What
is all the stuff
that the “stuff” is
made of?
What’s the
evidence for all
this?
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In-Class Writing Assignment
Write down, during the
course of lecture,
Two questions you want
to know the answer to
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Papers for the Course
• There will be three papers for the
course
– http://faculty.physics.tamu.edu/
toback/109/WritingAssignments/
• Due dates are posted there
• Paper 1 will be assigned after we
start Chapter 9, due one week
after we finish Chapter 9
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In Class Quiz
Answer the following question:
Tell why the subject of “light” is
SO IMPORTANT that we spent
an entire on it
Make sure to include what we
learned that was so important
(AND WHY!!)
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Does this make sense?
Most objects we know and love (the
Earth, us etc.) have LOTS of
electrons and protons
• If EM is so much stronger than
Gravity why don’t we feel it?
• Why doesn’t the Earth feel the
electric charge of the electrons
and protons in the Sun?
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EM vs. Gravity
• Answer: Equal numbers of
protons and electrons
– Each atom/molecule is exactly
electrically neutral or they
would attract more charge to
make them so
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– Bottom line: Accelerating
charges emit photons, and
accelerating masses emit
gravity “waves.” Can’t explain
atoms in your body that “live
for years”
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What’s different?
•Gravity:
– All objects attract no matter what
– (As far as we know…)
•ElectroMagnetism:
Like charges repel each other
Opposite charges attract each other
– Ignores neutral particles
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Only Orbits with Specific
Wavelengths Work
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• This is some
text
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