Physics We Need Topic 3: Quantum Mechanics and Atoms Big Bang, Black Holes, No Math 1 Big Bang,...

Physics We NeedTopic 3: Quantum Mechanics and

Atoms

Big Bang, Black Holes, No Math

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ASTR/PHYS 109Dr. David TobackLecture 10, 11 &

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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 turnitin on eCampus


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– Let us know if you have been misgraded– Unit 1 Revision: Grades posted soon (still

doing regrades)– Unit 2 Revision (if desired): Stage 2


• Paper 1: – Stage 1 due Monday before class– MUST submit to turnitin on eCampus

• Honors Paper:– Stage 0 due today


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– 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


• 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 5


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Papers in CPR/ScheduleSchedule 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 chapter3.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 later6.If you did a Stage 1, Calibrations/Reviews/Self-

Assessment due one week after that

6


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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/t

oback/109/WritingAssignments/samplepaper.shtml

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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 9


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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 1: Text due 10/1 (Ch 6)•Paper 2: Text due 10/15 (Ch 8)•Paper 3: Text due 11/1 (Ch 12)•Paper 4: Text due 11/15 (Ch 17)

•Honors Stage 0 (not in CPR): Due 10/6

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So Far

Topics1.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 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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Chapter 8

Different Types of Atoms• 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)

•The Strong Force– Keeps protons and neutrons together– Different types of nuclei different types of atoms – 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 light we see from the stars

ThisLecture

NextLecture


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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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The experiment gives results like #2!

Early evidence for the Atomic Model

Shoot atoms at a “target”

Bag stuffed with cotton and a few small rocks

The positive charge in an atom and most of its mass is concentrated in a tiny, very dense center: The Nucleus

Bag stuffed with cotton

Theory:

1?

2?

Experiment (1910’s):


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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 electron


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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•Neutrons•Protons–Neutrons and Protons are really made of quarks•Discovered in the 1970’s •We’ll talk more about this in the next chapter

Talked about this in Chapter 3More in Chapter

8


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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

ThisLecture

NextLecture


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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

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 attractionPhysics 202

Physics 208

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 attractionPhysics 201Physics 218


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•Gravity: –All objects attract no matter what –(As far as we know…)

•ElectroMagnetism:

–Ignores neutral particles

What’s different?


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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: Hydrogen

One electron and one proton

(Partially wrong)

+

-

| ~10-10 m |

| |

~10-15 m

Figure not to scale


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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

ThisLecture

NextLecture


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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 MechanicsTwo 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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•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 nucleusLower Energy

and closer to

the nucleus

Only these levels are allowed!


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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)Higherb)Lowerc)Same


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Clicker Question

After a collision with a stationary atom, the speed of a photon is

a)Higherb)Lowerc)Same


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Clicker Question

After a collision with a stationary atom, the wavelength of a photon is

a)Longerb)Shorterc)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

- -

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

1: Two electrons hanging out


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A Proton and Electron

- +

2: Proton on the right “emits” a photon and “recoils”

3: Photon bangs into the electronDoesn’t transfer Momentum

Transfers information on how to moveOpposite signs attract

For those of you who know a little bit, this is how “electric fields” work

1: A proton and an electron hanging out


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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

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-

Electron can “absorb” a photon Electron becomes more energetic


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Electron Emitting a Photon

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-

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

energetice

e

Electron can “emit” a photon becomes less

energetice

e


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Feynman Diagram for an Atom

•A diagram of how the particles “talk” to each other

•These two are attracted

Hydrogen Atom

e-

PP

e-


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If a photon with the right energy hits an atom and is absorbed, the electron can “jump” to an “excited state” 59

Photon and Atom


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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 the two states

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Excited Atom Emits a Photon


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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 Lowest

Energy State

Proton

Atom in a Higher

Energy State


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An Excited Atom Emits a Photon

Photon with a

specific energy

Atom in a high Energy

State

Atom in Lowest State


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Absorbing and Emitting a Photon

http://bigbang.physics.tamu.edu/Figures/StolenAnimations/bohr.swf


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Lots of Different Energy States

http://bigbang.physics.tamu.edu/Figures/StolenAnimations/BohrAtom.avi


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Photons and AtomsPhotons can interact with Atoms in three

ways1.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?

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• 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

colors will be absorbed!

Atomic Fingerprinting


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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:



• 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


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– 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 (up-to 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)Nothingb)It would get smallerc)It would get biggerd)It would disappeare)None of the above 75


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Clicker QuestionWhat 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 youc)Objects behind you would be

gravitationally lensedd)Your body would barely noticee)You would die like you would if you

got shot with any kind of bullet

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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 massc)Because it is made of black holes

d)Because it doesn’t interact with light 77


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Clicker Question

As far as we know, Dark Matter exists:

a)Everywhere in the universe

b)Only near black holesc)Mostly in or around galaxies

d)It doesn't existe)We don't know where it 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 QuestionInstead 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: Speeda) The speed of the photon stays the sameb) The speed of the photon slows down like a rock would

Question 2: Energya) 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: Colora) The color of the photon stays the sameb) 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 QuestionA 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 electronb)Yes, it was bouncing around inside the atomc)No, the electron destroyed the original photon

and created the new photond)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 course82


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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

e

e

Electron can “emit” a photon becomes less

energetic

e

e


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• Paper 1: – Stage 1 due Monday before class– Can submit a draft for feedback on

eCampus if you like– MUST submit to 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

Wrong energy

•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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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 can come out


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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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•The electron “wave” has to go all the way around

•Can “wave” once, twice, three times etc… –A quantized number


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•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:

–Ignores neutral particles

Like charges repel each otherOpposite charges attract each other


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•This is some text


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Physics We Need Topic 3: Quantum Mechanics and Atoms Big Bang, Black Holes, No Math 1 Big Bang,...

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