Big
g Bang,
ang, Black
ac
Holes No Math
Holes,
ASTR/PHYS
AS
R/PHYS 109
09
Dr. Dav
David
d Toback
oback
Lecture 9 & 10
Physics We Need
Big Bang, Black
Holes, No Math Topic 3: Quantum Mechanics and Atoms
1
Was Due for Today – L10
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture
P
L t
R
Reading
di Q
Questions:
ti
– Unit 1 Revision (if needed): Stage 2 due before class
– Unit 2 Revision (if desired): Stage 2 due before class
• Let
L us know
k
if
f you were misgraded
d d
• End-of-Chapter Quizzes:
– Chapter 6
• Paper 1:
– Stage 1 due Monday before class in CPR
– Can submit a draft for feedback on eCampus if you
like before Thursday at 11:55PM
• Will do our best for late submissions
Physics We Need
Big Bang, Black
Holes, No Math Topic 3: Quantum Mechanics and Atoms
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Taken from CPR for Paper 1
Physics We Need
Big Bang, Black
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So Far
Topics
1 Li ht and
1.Light
d D
Doppler
l Shifts
Shift  Done
D
2.Gravity,
y General Relativity
y and
Dark Matter Done
3.Atomic Physics and Quantum
Mechanics  Now
4 Nuclear Physics and Chemistry
4.Nuclear
5.Temperature and Thermal
E ilib i
Equilibrium
Physics We Need
Big Bang, Black
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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
f small
m ll things
thin
• Small things:
g The Fundamental
Building Blocks of Nature
–What is the “stuff”
stuff in
atoms?
Physics We Need
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The Largest Stuff
• Most of the light we see
from space
p
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
Physics We Need
same?
Big Bang, Black
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How do Atoms work?
• ElectroMagnetism (electric charge)
– What
Wh t holds
h ld electrons
l t
and
d protons
t
together
• Quantum Mechanics
– The f
funny
y way
y atoms
m form
f m
– Electrons in orbits
– Atoms absorbing and emitting
photons (light)
Chapter 7
Physics We Need
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Different Types of Atoms
Chapter 8
• The Strong Force
– Keeps protons and neutrons together
in the atomic nucleus
Different
ff
types
yp of
f nuclei
–D
 different types of atoms
– Different atoms  Different light…
• Nuclear Physics and Chemistry
• Studying the Stars using their light
– Spectral
Sp t l li
lines of
f the
th atoms
t m
– Atomic “fingerprints”
– The light we see from the stars
Physics We Need
Big Bang, Black
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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
stuff in atoms
– What is the “stuff”
• ElectroMagnetism (electric charge)
– What holds electrons and protons together
• Quantum Mechanics
– Why
Wh atoms f
form the
h way they
h
do
d
– Electron in orbits
– Atoms absorbing and emitting photons (light)
This
Thi
Lecture
• The Strong Force
– Keeps protons and neutrons together
Next
– Different types of nuclei  different types of atoms
Lecture
– Different
Diff
t atoms
t
 Different
Diff
t li
light…
ht
• Nuclear Physics and Chemistry Different TYPES of Atoms
• Studying the Stars using their light
p
lines of
f the atoms
m
– Spectral
– Atomic “fingerprints”
– The Black
light we see from Physics
the stars
We Need
Big Bang,
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Holes, No Math Topic 3: Quantum Mechanics and Atoms
The Fundamental Building Blocks
Our best understanding:
The
h very
ry BIG
G stuff iss
made up of LOTS of
very small stuff
Need to understand:
1. What are the
g
fundamental building
blocks
bl k of
f nature
2. How it’s all held
together
3. How they “create” the
light we see
Physics We Need
Big Bang, Black
Holes, No Math Topic 3: Quantum Mechanics and Atoms
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Early evidence for the Atomic Model
Shoot atoms at a “target”
Theory:
Theory
Experiment
(1910’s):
1?
Bag stuffed with cotton
2?
Bag stuffed with cotton and a few
small
ll rocks
k
The experiment gives
results
l like
l k #2!
# !
The positive charge in an atom and most of its mass is
concentrated
t t d iin a ti
tiny, very dense
d
center:
t
Th Nucleus
The
N l
Physics We Need
Big Bang, Black
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The Building Blocks of Nature
In the 19-teens
and 20
20’ss
experiments
m
determined:
• Atoms are made
f a nucleus
of
surrounded by
electrons
– Many types of
nuclei
–
Only
one
kind
of
Physics We Need
Big Bang, Black
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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
N l
is
i composed
d of
f
neutrons and protons
• Number of p
protons and
neutrons in the nucleus
determines the atom type
Physics We Need
Big Bang, Black
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The Fundamental Building Blocks of Nature
• Electrons
Talked about this
• Neutrons
N t
in Chapter 3
More in Chapter 8
• Protons
– Neutrons and Protons are
really made of quarks
•Discovered in the 1970’s
•We
W ’ll
ll talk
t lk m
more about
b t this
thi in
the next chapter
Physics We Need
Big Bang, Black
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Putting Them Together
How do we p
put these
fundamental building
blocks together to
f
form
atoms?
?
Physics We Need
Big Bang, Black
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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”
stuff in atoms
• ElectroMagnetism (electric charge)
– What holds electrons and protons together
• Quantum Mechanics
– Why
Wh atoms
t
form
f
the
th way they
th
do
d
– 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
Physics We Need
Big Bang, Black
Holes, No Math Topic 3: Quantum Mechanics and Atoms
This
Lecture
Next
Lecture
L
u
24
ElectroMagnetism
• You probably already
know that protons and
electrons have
“electric”
electric charges
• Positive charge and
negative
ti charge
h
attract
tt
t
each other
• Call this
g
ElectroMagnetism
+
-
Physics We Need
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Weirdness…
You probably never
th
thought
ht about
b t it
this way but in
many ways the
way
y things
g with
electric charge
attract is the
same as in gravity
+
-
Physics We Need
Big Bang, Black
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Gravity vs. ElectroMagnetism
Gravity
• Every
y object
j
in the
universe attracts
every other object in
the universe
• The bigger the mass,
the bigger the
attraction
• The further the
di t
distance
b
between
t
th
the
objects, the smaller
the attraction
ElectroMagnetism
• Every
y charged
g
object
j
in the universe
“attracts” every other
g
object
j
in the
charged
universe
• The bigger the charge,
the bigger the
attraction
• The further the
distance between the
objects, the smaller
the attraction
Physics 202
Physics 201
Physics We Need
Big Bang, Black
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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:
El t M
ti
– Ignores neutral particles
Physics We Need
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Other Differences
•ElectroMagnetism is MUCH
stronger
t
th
than gravity
it
If I have two electrons,
electrons the
•If
electric force between them is
so powerful
f l that
th t it iis 1042 times
ti
stronger
g than gravity
g
y
–Can “ignore” gravity inside
atoms
t
Physics We Need
Big Bang, Black
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Aside
• ElectroMagnetism is MUCH
weaker than the Strong Force
• For two q
quarks inside a p
proton
the Strong Force is ~100
times stronger than the EM
force
– Can almost “ignore”
ignore EM
inside protons
Physics We Need
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Atomic Physics
How do we make up atoms?
1.Start with a simple (partially
(
g) atomic model
wrong)
– Positive Nucleus attracts the
negatively charged electrons
and keeps them in “orbit”
2.Then move to the weird world
of Quantum Mechanics
Physics We Need
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A Hydrogen Atom
The simplest
atom:
Figure not
to scale
-
Hydrogen
One electron
and one
proton
(Partially wrong)
|
+
|
15 m
~10-15
|
10 m
~10
10-10
Physics We Need
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|
32
Is the world this simple?
• This is a nice simple model
• Why
Wh does
d
the
h electron
l
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
Physics We Need
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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
we d have nothing: No
atoms!
Would take ~10 picoseconds (10-11s)
–Would
Physics We Need
Big Bang, Black
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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
p
be able to be almost
their speed,
anywhere near the nucleus (like a
planet or a comet))
p
• Don’t observe this… Only specific
distances from the nucleus
Physics We Need
Big Bang, Black
Holes, No Math Topic 3: Quantum Mechanics and Atoms
35
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”
ff in atoms
• ElectroMagnetism (electric charge)
– What holds electrons and protons together
• Quantum Mechanics
– Why
y atoms form the way
y they
y 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…
g
• Studying the Stars using their light
– Spectral lines of the atoms
– Atomic “fingerprints”
g we see from the stars
– The light
Physics We Need
Big Bang, Black
Holes, No Math Topic 3: Quantum Mechanics and Atoms
This
Lecture
Next
Lecture
L
u
36
Quantum Mechanics
• How do we explain these weird
ffeatures
t
th
thatt we observe
b
about
b t
Atoms?
• Quantum Mechanics!
• LOTS we COULD say about QM,
QM
but since we could spend years on
this
hi we’ll
’ll focus
f
only
l on the
h most
important points you need
Physics We Need
Big Bang, Black
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Quantum Mechanics
Two big issues:
1.. All particles
part c
can be described
cr
both
th as
a
particles AND waves
– Saw this for photons
– True
T
for
f electrons
l t
(and
( d protons
t
etc.)
t ) also!
l !
2. In atoms: Electrons can ONLY be in one of
the ava
available
lable energy states, and at certa
certain
n
distances from the nucleus
– Keep atoms from collapsing! (Good!)
– “Quantizes”
“Q
ti
” the
th interactions
i t
ti
with
ith li
light
ht ii.e.
only some energy photons interact with
atoms
Physics We Need
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Energy of Electron Waves
• Small energy
gy
electron have
large
wavelengths
• Small
wavelength
electrons have
l
large
energy
Physics We Need
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Only Orbits with Specific Wavelengths Work
• The electron “wave”
has to go all the way
around
• Can
C
have
h
one
peak/trough, two
peaks/troughs,
k /t
h three
th
peaks/troughts etc…
– A quantized number
– The Q
Quantum in
Quantum Mechanics
Physics We Need
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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
Physics We Need
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Energy and Distance from The Nucleus
Higher
g
Energy and
further away
y
from the
nucleus
Lower
Energy and
closer to
the nucleus
Big Bang, Black
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Only these levels
Physics We Need
42
are
allowed!
Topic 3: Quantum Mechanics and
Atoms
Prep For Next Time – L10
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture
Pre Lecture Reading Questions:
– Let us know if you have been misgraded
• End-of-Chapter Quizzes:
– If we finished Chapter 7 then End-of-Chapter
End of Chapter Quiz 7a &
7b (else, just through Chapter 6)
• Paper 1:
– Stage
St
1 due
d
M d
Monday
before
b f
class
l
in
i CPR and
d turnitin
t
iti on
eCampus
– Can submit a draft for feedback on eCampus if you like
b f
before
Thursday
Th d
att 11:55PM
11 55PM
• Will do our best for late submissions
• Honors Paper:
– Stage 0 due October 5th before class
Physics We Need
Big Bang, Black
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Holes, No Math Topic 3: Quantum Mechanics and Atoms
Full set of Readings So Far
•Required:
– BBBHNM:
BBBHNM Chap
Ch
1-9
1 9
•Recommended:
– BHOT: Chap. 1-6, 9 and 11
(117 122)
(117-122)
– SHU: Chap. 1-3, 6 and 7 (upto page 153)
– TOE: Chap. 1
Physics We Need
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Holes, No Math Topic 3: Quantum Mechanics and Atoms
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