Transcript phys1444-fall11-083011

PHYS 1444 – Section 003
Lecture #2
Tuesday, Aug. 30, 2011
Dr. Jaehoon Yu
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Some basics …
Chapter 21
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Static Electricity and Charge Conservation
Charges in Atom
Today’s homework is homework #2, due 10pm, Tuesday, Sept. 6!!
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PHYS 1444-003, Fall 2011 Dr. Jaehoon
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Announcements
• Plea to you: Please turn off your cell-phones,
pagers and computers in the class
• Reading assignment #1: Read and follow through
all sections in appendix A by Tuesday, Aug. 30
– A-1 through A-7
• There will be a quiz on this and Ch. 21 on
Thursday, Sept. 1.
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Who am I?
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Name: Dr. Jaehoon Yu (You can call me Dr. Yu)
Office: Rm 342, Chemistry and Physics Building
Extension: x22814, E-mail: [email protected]
My profession: High Energy Particle Physics (HEP)
– Collide particles (protons on anti-protons or electrons on anti-electrons,
positrons) at the energies equivalent to 10,000 Trillion degrees
– To understand
• Fundamental constituents of matter
• Forces between the constituents (gravitational, electro-magnetic, weak and
strong forces)
• Origin of Mass
• Creation of Universe (Big Bang Theory)
– A pure scientific research activity
• Direct use of the fundamental laws we find may take longer than we want but
• Indirect product of research contribute to every day lives; eg. WWW
– Why do we do with this?
• Make our everyday lives better
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Accelerators are Powerful Microscopes.
They make high energy particle beams
that allow us to see small things.
seen by
low energy beam
(poorer resolution)
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seen by
high energy beam
(better resolution)
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Accelerators are also Time Machines.
They make particles last seen
in the earliest moments of the universe.
anti-particle beam
particle beam
Energy
energy
energy
Particle and anti-particle annihilate.
E=
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2
mc
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Structure of Matter
Matter
Molecule
Atom
Nucleus
Baryon
Quark
(Hadron)
u
10-14m
10-9m
10-10m
10-2m
Condensed matter/Nano-Science/Chemistry
Atomic Physics
Nuclear
Physics
10-15m
protons, neutrons,
mesons, etc.
p,W,L...
<10-19m
top, bottom,
charm, strange,
up, down
Electron
(Lepton)
<10-18m
High Energy Physics
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The Standard Model
• Assumes the following fundamental structure:
Discovered
in 1995
Directly
observed in
2000
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Fermilab Tevatron and
LHC
at
CERN
• World’s Highest Energy p-p collider
World’s Highest Energy proton-anti-proton collider
– 27km circumference, 100m underground
– Design Ecm=14 TeV (=44x10-7J/p 362M
Joules on the area less than 10-4m2)
 Equivalent to the kinetic energy of a B727
(80tons) at the speed 193mi/hr  312km/hr
– 6km circumference
– Ecm=1.96 TeV (=6.3x10-7J/p 13M Joules on 104m2)
– Equivalent to the kinetic energy of a 20t truck at the
speed 81mi/hr 130km/hr
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~100,000 times the energy density at ground 0 of the atom
bomb dropped on Hiroshima
– To be shut down Sept. 30, 2011
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Chicago
CDF
p
Tevatron
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~3M times the energy density at ground 0 of atom
bomb dropped on Hiroshima
First 7TeV collisions on 3/30/10  The highest energy
humans ever achieved!!
• First collisions in 2011 in mid March, 2011
DØ
p
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A Future Linear Collider
• An electron-positron collider on a straight line for precision
measurements
• CMS Energy: 0.5 – 1 TeV
• 10~15 years from now
• Takes 10 years to build the accelerator and the detector
L~31km
Circumference ~6.6km
~300 soccer fields
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DØ Detector
ATLAS Detector
30’
50’
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Weighs 5000 tons and 5 story tall
Can inspect 3,000,000 collisions/second
Record 100 collisions/second
Records approximately 10,000,000
bytes/second
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Records 0.5x10 (500,000,000,000,000) bytes
per year (0.5 PetaBytes).
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Weighs 7000 tons and 10 story tall
Can inspect 1,000,000,000 collisions/second
Records 200 – 400 collisions/second
Records approximately 350,000,000
bytes/second
Record 2x1015 (2,000,000,000,000,000) bytes
each year (2 PetaByte).  200*Printed
material of the US Lib. of Congress
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DØ Central Calorimeter 1990
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Computers put together a picture
`p
p
Digital data
Data Reconstruction
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Highest ET dijet event at DØ
CH
hadrons
FH

EM
p
K
Time
“parton jet” “particle jet” “calorimeter jet”
How does an Event Look in a Collider Detector?
q
g
E1T  475 GeV, 1  0.69
p
p
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q
E1T  472 GeV, 2  0.69
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GEM Application Potential
FAST X-RAY IMAGING
Using the lower GEM signal, the
readout can be self-triggered with
energy discrimination:
9 keV absorption
radiography of a small
mammal (image size ~
60 x 30 mm2)
A. Bressan et al,
Nucl. Instr. and Meth. A 425(1999)254
F. Sauli, Nucl. Instr. and Meth.A 461(2001)47
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Information & Communication Source
• My web page: http://www-hep.uta.edu/~yu/
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Contact information & Class Schedule
Syllabus
Homework
Holidays and Exam days
Evaluation Policy
Class Style & Communication
Other information
• Primary communication tool is e-mail: Make sure that your e-mail
address at the time of the registration is your most favorite
primary one.
– Will send a test message this afternoon.
– Please reply just to “me” for confirmation of the communication.
•
3 point extra credit if done just to ME by 11pm Friday, tomorrow.
• Office Hours: 2:00 – 3:00pm, Tuesdays and Thursdays or by
appointments
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• Homework: 25%
• Exams
Evaluation Policy
– Midterm and Final Comprehensive Exams (10/20 and 12/15): 19% each
– One better of the two term Exams: 12%
• Total of two non-comprehensive term exams (9/29 and 11/22)
• One better of the two exams will be used for the final grade
• Missing an exam is not permissible unless pre-approved
– No makeup test
– You will get an F if you miss any of the exams without a prior approval
• Lab score: 15%
• Pop-quizzes: 10%
100%
• Extra credits: 10% of the total
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Random attendances
Physics department colloquium participation
Strong participation in the class discussions
Special projects
Planetarium shows and Other many opportunities
• Grading will be done on a sliding scale
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Homework
Solving homework problems is the only way to comprehend class
material
• An electronic homework system has been setup for you
– Details are in the material distributed today and on the web
– https://quest.cns.utexas.edu/student/courses/list
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Choose the course PHYS1444-003, unique number 44003
Download homework #1, solve the problems and submit them online
Multiple unsuccessful tries will deduct points
Roster will close Tuesday, Aug. 30
You need a UT e-ID: Go and apply at the URL
https://idmanager.its.utexas.edu/eid_self_help/?createEID&qwicap-pageid=EA027EFF7E2DA39E if you don’t have one.
• Each homework carries the same weight
• ALL homework grades will be used for the final grade
• Home work will constitute 25% of the total  A good way of keeping
your grades high
• Strongly encouraged to collaborate  Does not mean you can copy
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Attendances and Class Style
• Attendances:
– Will be taken randomly
– Will be used for extra credits
• Class style:
– Lectures will be on electronic media
• The lecture notes will be posted on the web AFTER each class
– Will be mixed with traditional methods
– Active participation through questions and discussions are
STRONGLY encouraged  Extra credit….
– Communication between you and me is extremely
important
• If you have problems, please do not hesitate talking to me
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• Physics Labs:
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Lab and Physics Clinic
Starts Tuesday, Sept. 6
Important to understand physical principles through experiments
15% of the grade
Lab syllabus is available in your assigned lab rooms.
• Go by the lab room between 8am - 6pm M – F and pick up the syllabus
• Physics Clinic:
– Free service
– They provide general help on physics, including help solving homework problems
• Do not expect solutions of the problem from them!
• Do not expect them to tell you whether your answers are correct!
• It is your responsibility to make sure that you have done everything correctly!
– 11am – 6pm, Mon – Fri and 12 – 6pm Sat. in SH 007
– This service begins Thursday, Sept. 1
• Addition help: Supplemental Instruction: Husain Lohawala
– 2:30 – 3:30pm, Mondays and Wednesdays in SH333
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Extra credit
• 10% addition to the total
– Could boost a B to A, C to B or D to C
• What constitute for extra credit?
– Random attendances
– Physics department colloquium participation
• Some will be double or triple credit (
– Strong participation in the class discussions
– Special projects
– Watch the valid planetarium shows
– Many other opportunities
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Valid Planetarium Shows
Regular running shows
– We are Astronomers
– Nanocam: Trip into Biodiversity
• Shows that need special arrangements
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Black Holes
Ice Worlds
Magnificent Sun
Stars of the Pharaohs
Time Space
Two Small Pieces of Glass
SOFIA
Violent Universe
How to submit for extra credit?
– Obtain the ticket stub that is signed and dated by the planetarium star lecturer of
the day
– Collect the ticket stubs
– Tape all of them on a sheet of paper with your name and ID written on it
– Submit the sheet at the end of the semester when asked
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What can you expect from this class?
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All A’s?
– This would be really nice, wouldn’t it?
– But if it is too easy it is not fulfilling or meaningful….
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This class is not going to be a stroll in the park!!
You will earn your grade in this class.
– You will need to put in sufficient time and sincere efforts
– Exams and quizzes will be tough!!
• Sometimes problems might not look exactly like what you learned in the class
• Just putting the right answer in free response problems does not work!
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But you have a great control of your grade in your hands
– Homework is 25% of the total grade!!
• Means you will have many homework problems
– Sometimes much more than any other classes
– Sometimes homework problems will be something that you have yet to learn in class
– Exam’s problems will be easier that homework problems but same principles!!
– Lab 15%
– Extra credit 10%
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I will work with you so that your efforts are properly rewarded
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What do we want to learn in this class?
• Physics is everywhere around you.
• Skills to understand the fundamental principles that surrounds
you in everyday lives…
• Skills to identify what laws of physics applies to what
phenomena and use them appropriately
• Understand the impact of physical laws and apply them
• Learn skills to think, research and analyze observations.
• Learn skills to express observations and measurements in
mathematical language
• Learn skills to express your research in systematic manner in
writing
• But most importantly the confidence in your physics ability
and to take on any challenges laid in front of you!!
Most importantly,
let us
have
a lot of FUN!!
PHYS 1444-003,
Fall 2011
Dr. Jaehoon
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In this course, you will learn…
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Electricity and Magnetism
Electric and Magnetic Forces
Electric charge and magnetic poles
Electric and magnetic potential and energies
Propagation of electric and magnetic fields
Relationship between electro-magnetic forces
and light
• Behaviors of light and optics
• Special relativity and quantum theories
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Brief History of Physics
• AD 18th century:
– Newton’s Classical Mechanics: A theory of mechanics based on
observations and measurements
• AD 19th Century:
– Electricity, Magnetism, and Thermodynamics
• Late AD 19th and early 20th century (Modern Physics Era)
– Einstein’s theory of relativity: Generalized theory of space, time, and energy
(mechanics)
– Quantum Mechanics: Theory of atomic phenomena
• Physics has come very far, very fast, and is still progressing, yet
we’ve got a long way to go
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What is matter made of?
How do matters get mass?
How and why do matters interact with each other?
How is universe created?
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Needs for Standards and Units
• Three basic quantities for physical measurements
– Length, Mass, and Time
• Need a language that everyone can understand each
other
– Consistency is crucial for physical measurements
– The same quantity measured by one must be comprehendible
and reproducible by others
– Practical matters contribute
• A system of unit called SI (System International)
established in 1960
– Length in meters (m)
– Mass in kilo-grams (kg)
– Time in seconds (s)
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SI Base Quantities and Units
Quantity
Length
Time
Mass
Electric current
Temperature
Amount of substance
Luminous Intensity
Unit
Meter
Second
Kilogram
Ampere
Kelvin
Mole
Candela
Unit Abbrevation
m
s
kg
A
k
mol
cd
•There are prefixes that scales the units larger or smaller for convenience (see pg. 7)
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Prefixes, expressions and their meanings
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deca (da): 101
hecto (h): 102
kilo (k): 103
mega (M): 106
giga (G): 109
tera (T): 1012
peta (P): 1015
exa (E): 1018
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deci (d): 10-1
centi (c): 10-2
milli (m): 10-3
micro (m): 10-6
nano (n): 10-9
pico (p): 10-12
femto (f): 10-15
atto (a): 10-18
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How do we convert quantities from one
unit to another?
Unit 1 = Conversion factor X Unit 2
1 inch
1 inch
1 inch
1 ft
2.54
0.0254
2.54x10-5
30.3
cm
m
km
cm
1 ft
1 ft
1 hr
0.303
3.03x10-4
60
M
km
minutes
1 hr
And many
3600
More
seconds
Here….
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Static Electricity; Electric Charge and
Its Conservation
• Electricity is from Greek word elecktron=amber, a petrified
tree resin that attracts matter if rubbed
• Static Electricity: an amber effect
– An object becomes charged or “posses a net electric charge”
due to rubbing
– Can you give some examples?
• Two types of electric charge
– Like charges repel while unlike charges attract
– Benjamin Franklin referred the charge on glass
rod as the positive, arbitrarily. Thus the charge
that attracts glass rod is negative.  This
convention is still used.
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Static Electricity; Electric Charge and
Its Conservation
• Franklin argued that when a certain amount of charge is
produced on one body in a process, an equal amount of
opposite type of charge is produced on another body.
– The positive and negative are treated algebraically so that during any
process the net change in the amount of produced charge is 0.
• When you comb your hair with a plastic comb, the comb acquires a negative
charge and the hair an equal amount of positive charge.
• This is the law of conservation of electric charge.
– The net amount of electric charge produced in any process is
ZERO!!
• If one object or one region of space acquires a positive charge, then an equal
amount of negative charge will be found in neighboring areas or objects.
• No violations have ever been observed.
• This conservation law is as firmly established as that of energy or momentum.
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Electric Charge in the Atom
• It has been understood through the past century that an atom
consists of
– A positively charged heavy core  What is the name?
• This core is nucleus and consists of neutrons and protons.
– Many negatively charged light particles surround the core  What
is the name of these light particles?
• These are called electrons
• How many of these?
As many as the number of protons!!
• So what is the net electrical charge of an atom?
– Zero!!! Electrically neutral!!!
• Can you explain what happens when a comb is rubbed on a
towel?
– Electrons from towel get transferred to the comb, making the comb
negatively charged while leaving positive ions on the towel.
– These charges eventually get neutralized primarily by water
molecules in the air.
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Insulators and Conductors
• Let’s imagine two metal balls of which one is charged
• What will happen if they are connected by
– A metallic object?
• Some charge is transferred.
• These objects are called conductors of electricity.
– A wooden object?
• No charge is transferred
• These objects are called nonconductors or insulators.
• Metals are generally good conductors whereas most other
materials are insulators.
– There are third kind of materials called, semi-conductors, like silicon
or germanium  conduct only in certain conditions
• Atomically, conductors have loosely bound electrons while
insulators have them tightly bound!
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Induced Charge
• When a positively charged metal object is brought
close to an uncharged metal object
– If the objects touch each other, the free electrons in the
neutral ones are attracted to the positively charged
object and some will pass over to it, leaving the neutral
object positively charged.
– If the objects get close, the free electrons in the neutral
ones still move within the metal toward the charged
object leaving the opposite of the object positively
charged.
• The charges have been “induced” in the opposite ends of the
object.
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Induced Charge
ground
• We can induce a net charge on a metal object by
connecting a wire to the ground.
– The object is “grounded” or “earthed”.
• Since it is so large and conducts, the Earth can give or
accept charge.
– The Earth acts as a reservoir for charge.
• If the negative charge is brought close to a neutral metal
– The positive charges will be induced toward the negatively
charged metal.
– The negative charges in the neutral metal will be gathered on the
opposite side, transferring through the wire to the Earth.
– If the wire is cut, the metal bar has net positive charge.
• An electroscope is a device that can be used for
detecting charge and signs.
– How does this work?
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Coulomb’s Law
• Charges exert force to each other. What factors affect the
magnitude of this force?
– Any guesses?
• Charles Coulomb figured this out in 1780’s.
• Coulomb found that the electrical force is
– Proportional to the multiplication of the two charges
• If one of the charges doubles, the force doubles.
• If both the charges double, the force quadruples.
– Inversely proportional to the square of the distances between them.
– Electric charge is a fundamental property of matter, just like mass.
• How would you put the above into a formula?
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Coulomb’s Law – The Formula
Q11
Q22
Q
F
2
r
Formula
Q1Q2
F k
2
r
• Is Coulomb force a scalar quantity or a vector quantity? Unit?
– A vector quantity. Newtons
• Direction of electric (Coulomb) force is always along the line joining
the two objects.
– If the two charges are the same: forces are directed away from each other.
– If the two charges are opposite: forces are directed toward each other.
• Coulomb force is precise to 1 part in 1016.
• Unit of charge is called Coulomb, C, in SI.
• The value of the proportionality constant, k, in SI
unit is k  8.988  109 N  m2 C 2
• Thus, 1C is the charge that gives F~9x109N of
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1444-003,
2011 Dr.other.
Jaehoon
force when
placed 1m PHYS
apart
fromFall
each
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Electric Force and Gravitational Force
Q1Q2
F k
2
r
Extremely
Similar
M1M 2
F G
2
r
• Does the electric force look similar to another force? What is it?
– Gravitational Force
• What are the sources of the forces?
– Electric Force: Charges, fundamental properties of matter
– Gravitational Force: Masses, fundamental properties of matter
• What else is similar?
– Inversely proportional to the square of the distance between the sources of the
force  What is this kind law called?
• Inverse Square Law
• What is the difference?
– Gravitational force is always attractive.
– Electric force depends on the type of the two charges.
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The Elementary Charge and Permittivity
• Elementary charge, the smallest charge, is that of an
electron: e  1.602  1019 C
– Since electron is a negatively charged particle, its charge is –e.
• Object cannot gain or lose fraction of an electron.
– Electric charge is quantized.
• It changes always in integer multiples of e.
• The proportionality constant k is often written in terms of
another constant, e0, the permittivity of free space. They
are related k  1 4pe 0 and e 0  1 4p k  8.85 1012 C 2 N  m2.
1 Q1Q2
• Thus the electric force can be written: F  4pe r 2
0
• Note that this force is for “point” charges at rest.
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Example 21 – 1
• Electric force on electron by proton. Determine the
magnitude of the electric force on the electron of a
hydrogen atom exerted by the single proton (Q2=+e) that
is its nucleus. Assume the electron “orbits” the proton at
its average distance of r=0.53x10-10m.
Using Coulomb’s law
Each charge is
F
Q1Q2
Q1Q2

k
4pe 0 r 2
r2
1
Q1  e  1.602  1019 C and Q2  e  1.602 1019 C
So the magnitude of the force is
1.6 10 C 1.6 10
 0.53 10 m 
19
Q1Q2
9
2
2
F  k 2  9.0  10 N  m C
r
 8.2  10 8 N
Which direction?
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10
19
C

2
Toward each other…
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Example 21 – 2
• Which charge exerts greater force? Two
positive point charges, Q1=50mC and Q2=1mC, are
separated by a distance L. Which is larger in
magnitude, the force that Q1 exerts on Q2 or the
force that Q2 exerts on Q1?
Q1Q2
F12  k 2
What is the force that Q1 exerts on Q2?
L
Q2Q1
What is the force that Q2 exerts on Q1?
F21  k 2
L
Therefore the magnitudes of the two forces are identical!!
Well then what is different? The direction.
Which direction?
Opposite to each other!
What is this law?
Newton’s third law, the law of action and reaction!!
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