Download PHYS 1443 – Section 501 Lecture #1

PHYS 1444 – Section 001
Lecture #1
Tuesday June 5, 2012
Dr. Andrew Brandt, with Ian Howley and Ryan Hall
1. Introduction (longish) and Syllabus
2. Chapter 21
-Static Electricity and Charge Conservation
-Charges in Atom, Insulators and Conductors
&
Induced Charge
-Coulomb’s Law
Please turn off electrical devices in class
Thanks to Dr. Yu for bringing this class into 21st Century!
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
1
My Background+Research
B.S. Physics and Economics College of William&Mary 1985
PH.D. UCLA/CERN High Energy Physics 1992
(UA8 Experiment-discovered hard diffraction)
1992-1999 Post-doc and Lab Scientist at Fermi National Accelerator Laboratory
-1997 Presidential Award for contributions to diffraction
-Proposed and built (with collaborators from Brazil) DØ Forward Proton Detector
-Physics Convenor
-Trigger Meister
1999 Joined UTA as an Assistant Professor
2004 promoted to Associate Professor
2010 promoted to Full Professor
- Funding from NSF, DOE, and Texas approaching 10M$ as PI or Co-PI
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
2
My Main Research Interests
• High Energy Physics (aka Particle Physics)
• Physics with Forward Proton Detectors (detect protons
scattered at small angles)
• Fast timing detectors (How fast? Really really fast!)
http://www.youtube.com/watch?v=By1JQFxfLMM&feature=related
• Triggering (selecting the events to write to tape): at ATLAS
must choose most interesting 300 out of up to 40,000,000
events/sec
• Higgs Discovery
• Weapons of Mass Destruction (detection of)
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
3
Primary Web Page
http://www-hep.uta.edu/~brandta/teaching/su2012/teaching.html
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
4
Grading
• Exams: 3*20%
–
–
–
–
Two midterms and one final
Comprehensive final (some extra credit for incentive)
Exams will be curved if necessary
No makeup tests
• Homework: 20%
• Lab score: 20%
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
5
Homework
• Solving homework problems is the best (only?) way to
comprehend class material
• An electronic homework system has been setup
• Homework: will be done with Mastering Physics (can buy it with or
without text book (costs more but worth it!)
• http://www.masteringphysics.com/
• Course ID: MPBRANDT1444SU12
• First “assignment” due Saturday!!! It is meant to teach you how to
use mastering physics
• 2Nd (first real assignment) due next Tuesday—don’t blame me it
wasn’t my idea to take a summer class!
• How many of you are taking this class since it is required?
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
6
Mastering Physics Grades
• For grading purposes, some numeric answers to questions need to be exact.
For example, the answer to the question "How many days are in a week?" must be 7.
•The typical grading tolerance for most numeric answers in Mastering
assignment questions is between 2%-3%. For example, if the grading tolerance is
2% and the correct answer is 1043, both 1042 or 1045 are also graded as correct.
•When an answer is within tolerance, but doesn't match the correct answer: The
officially correct answer displays in a purple box (provided that Show Whether Answer
is Correct is set to Always). Students should use this answer if subsequent parts of an
assignment item require calculations based on this answer.
•Students should use at least three digits or significant figures in answers, unless
otherwise specified or unless the exact answer can be expressed using fewer than
three significant figures. If higher precision is required, or lower precision is allowed,
this is specified in the question or its instructions. When students must do multiple
calculations to get an answer they should use more significant figures than required
during each calculation and round off at the end
•You are allowed 6 attempts at a non multiple choice question (with each attempt
you lose some points). If you get a wrong answer: reread problem, could you
have made a sign error or a unit error or a round-off error?
Wednesday, Aug. 31,
2011
7
PHYS 1444-04 Dr.
Andrew Brandt
Attendance and Class Style
• Attendance:
– is STRONGLY encouraged, but I will not take
attendence
• Class style:
– Lectures will be primarily on electronic media
• The lecture notes will be posted AFTER each class
– Will be mixed with traditional methods
– Active participation through questions and
discussion are encouraged (chances are someone
else has the same question)
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
8
Structure of Matter
Matter
Molecule
Atom
Nucleus
Baryon
Quark
(Hadron)
u
cm
10-14m
10-9m
10-10m
Nano-Science/Chemistry
Atomic Physics
Nuclear
Physics
10-15m
<10-19m
top
protons, neutrons,
, bottom,
mesons, etc.
charm, strange,
p,W,L...
up, down
Electron
(Lepton)
<10-18m
High energy means small distances
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
High Energy Physics
9
Helium
Periodic Table
Neon
All atoms are made
of protons, neutrons
and electrons
u u
d
u
d d
Neutron
Proton
Gluons hold quarks together
Photons hold atoms together
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
Electron
10
What is High Energy Physics?
 Study of Matter/Forces at the most fundamental level.
 Great progress! The “STANDARD MODEL”
 BUT… many mysteries
=> Why so many quarks/leptons??
=> Why four forces?? Unification?
=> Where does mass come from??
=> Are there higher symmetries??
What is the “dark matter”??
Will the LHC create a black hole that destroys the Earth?
NO! See: http://public.web.cern.ch/Public/en/LHC/Safety-en.html
But if it did, it might look like:
http://www.youtube.com/watch?v=BXzugu39pKM
11
Role of Particle Accelerators
• Smash particles together
• Act as microscopes and time machines
– The higher the energy, the smaller object to be seen
– Particles that only existed at a time just after the Big
Bang can be made
• Two method of accelerator based experiments:
– Collider Experiments: protons, anti-protons,
electrons, muons?
– Fixed Target Experiments: Particles on a target
– Type of accelerator depends on research goals
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
12
Fermilab Tevatron and CERN LHC
• \ Highest Energy proton-antiproton collider
– Ecm=1.96 TeV (=6.3x10-7J/p
13M Joules on 10-4m2)
 Equivalent to the K.E. of a 20 ton
truck at a speed 81 mi/hr
Highest Energy (proton-proton)
collider since fall 2009
– Ecm=14 TeV (=44x10-7J/p
1000M Joules on 10-4m2)
 Equivalent to the K.E. of a 20 ton
truck at a speed 711 mi/hr
 Currently 8TeV collisions
Chicago

1500 physicists
130 institutions
30 countries
CDF
•
p
Tevatron
DØ
p
Fermilab: http://www.fnal.gov/ ; DØ: http://www-d0.fnal.gov/
5000 physicists
250 institutions
60 countries
CERN: http://www.cern.ch/ ; ATLAS: http://atlas.web.cern.ch/
DØ Detector
ATLAS Detector
30’
50’
•
•
•
•
•
•
Weighs 5000 tons
As tall as a 5 story building
Can inspect 3,000,000 collisions/second
Record 100 collisions/second
Records 10 Mega-bytes/second
Recording 0.5x1015 (500,000,000,000,000)
bytes per year (0.5 PetaBytes).
•
•
•
•
•
•
Weighs 10,000 tons
As tall as a 10 story building
Can inspect 1,000,000,000
collisions/second
Recors 200 -300 collisions/second
Records 300 Mega-bytes/second
Will record 2.0x1015
(2,000,000,000,000,000) bytes each year (2
PetaByte).
Tevatron: World’s 2nd Highest Energy Collider
Fermilab
DØ
High-tech fan
One of the DØ Forward Proton Detectors built
at UTA and installed in the Tevatron tunnel
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
15
Elastic Scattering Cross Section (FPD)
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
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ATLAS Forward Protons: A (10) Picosecond
Window on the Higgs Boson
A picosecond is a trillionth of a second.
This door opens ~once a second, if it opened
every 10 picoseconds it would open a hundred
billion times in one second (100,000,000)
Light can travel 7 times around the earth in
one second but can only travel 3 mm in 10 psec
Yes, I know it’s a door, not a window!
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
17
Forward Proton Fast Timing
WHY? Pileup Background Rejection
Ex: Two protons from one interaction and two b-jets from another
How?
Use time difference between protons to measure zvertex and compare with tracking z-vertex
measured with silicon detector
How Fast?
10 picoseconds is design goal
(light travels 3mm in 10 psec!)
gives large factor of background rejection
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
18
LeCroy Wavemaster
6 GHz Oscilloscope
Hamamatsu
PLP-10
Laser Power
Supply
Picosecond Test Facility
featuring initial
Undergraduate
Laser Gang (UGLG)
Undergraduate Laser Youths?
(UGLY)
You too can be UGLY (but
only if you are a physics
major)
[Don’t quote me on that!]
Tuesday, June 5, 2012
Laser Box
mirror
beam splitter
MCP-PMT
filter
lenses
PHYS 1444-001,19
Dr. Andrew Brandt
laser
Why Do Physics?
{
• To understand nature through experimental
Exp. observations and measurements (Research)
• Establish limited number of fundamental laws, usually
Theory with mathematical expressions
• Explain and predict nature
⇒Theory and Experiment work hand-in-hand
⇒Theory generally works under restricted conditions
⇒Discrepancies between experimental measurements
and theory are good for improvement of theory
⇒Modern society is based on technology derived from
detailed understanding of physics
{
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
20
Why Do Physics Part Deux
http://www.aps.org/publications/apsnews/200911/physicsmajors.cfm
2008/2009 Graduates
1.7% unemployment
While engineering
starting salaries are
typically higher than
physicists, mid-career
salaries are virtually
identical 101k$ for
engineering 99k$ for
physics
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
21
What Do Physicists Do?
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
22
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)
– Discovery of electron
– Einstein’s theory of relativity: Generalized theory of space, time, and energy
(mechanics)
– Quantum Mechanics: Theory of atomic phenomena (small distance scales)
• Physics has come very far, very fast, and is still progressing, yet
we’ve got a long way to go
– Particle physics and astrophysics final frontier?
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
23
Need for Standards and Units
• Three basic quantities for physical measurements
– Length, Mass, and Time
• Need a language so that people can understand each
other (How far is it to Chicago? 1000)
• Consistency is crucial for physical measurements
– The same quantity measured by one person must be
comprehensible and reproducible by others
• A system of unit called SI (System International)
established in 1960
– Length in meters (m)
– Mass in kilo-grams (kg)
– Time in seconds (s)
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
24
SI Base Quantities and Units
Quantity
Length
Time
Mass
Electric current
Temperature
Amount of substance
Luminous Intensity
Tuesday, June 5, 2012
Unit
Meter
Second
Kilogram
Ampere
Kelvin
Mole
Candela
Unit Abbrevation
m
s
kg
A
k
mol
cd
25
Prefixes and their meanings
•
•
•
•
•
•
•
•
deca (da): 101
hecto (h): 102
kilo (k): 103
mega (M): 106
giga (G): 109
tera (T): 1012
peta (P): 1015
exa (E): 1018
•
•
•
•
•
•
•
•
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
Impress your friends!
Tuesday, June 5, 2012
26
Examples 1.3 and 1.4 for Unit Conversions
• Ex 1.3: A silicon chip has an
area of 1.25in2. Express this
in cm2.
 2.54 cm 
1.25 in 2  1.25 in 2  

1
i
n


2


6
.
45
cm
2


 1.25 in  
2
 1 in

2
 1.25  6.45 cm 2  8.06 cm 2
• Ex 1.4: Where the posted speed limit is 65 miles per hour (mi/h or mph), what is this
speed (a) in meters per second (m/s) and (b) kilometers per hour (km/h)?
 12 in  2.54 cm   1 m 
1 mi=  5280 ft 
 1609 m  1.609 km


 1 ft  1 in   100cm 
 1609 m   1   1 h 
(a) 65 mi/h   65 mi  
  29.1 m/s
 
 
 1 mi   1 h   3600 s 
Oops, what
 1.609 km   1 
(b) 65 mi/h   65 mi  
 
  104 km/h about sig. figs.?
 1 mi   1 h 
Tuesday, June 5, 2012
27
About how fast did Usain run in MPH?
Uncertainties
• Physical measurements have limited precision,
no matter how good they are, due to:
Statistical { Number of measurements
Quality of instruments (meter stick vs micrometer)
Systematic
Experience of the person doing measurements
Etc.
{
In many cases, uncertainties are more important and
difficult to estimate than the central (or mean) values
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
28
Significant Figures
• Significant figures denote the precision of the
measured values
– Significant figures: non-zero numbers or zeros that are
not place-holders
• 34 has two significant digits; 34.2 has 3; 0.001 has one
because the 0’s before 1 are place holders, 34.100 has 5,
because the 0’s after 1 indicates that the numbers in these
digits are indeed 0’s.
• When there are many 0’s, use scientific notation:
– 31400000=3.14x107
– 0.00012=1.2x10-4
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
29
Significant Figures
• Operational rules:
– Addition or subtraction: Keep the smallest number of decimal
places in the result, independent of the number of significant
digits: 34.001+120.1=154.1
– Multiplication or Division: Keep the number of significant
figures of the operand with the least S.F. in the result:
34.001x120.1 = 4083, because the smallest number of
significant figures is 4.
– For homework may need to get this right!
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
30
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
– Example: Rub feet on carpet and zap your little sister
• Two types of electric charge
– Like charges repel while unlike charges attract
– Benjamin Franklin referred to the charge on a
glass rod as the positive, arbitrarily. Thus the
charge that attracts a glass rod is negative. 
This convention is still used.
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
31
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.
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
32
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 the 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.
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
33
Insulators and Conductors
• Picturetwo metal balls, one of which is charged
• What will happen if they are connected by
– A metallic object?
• Charge is transferred, until the charge is evenly distributed
• These objects are called conductors of electricity.
– A wooden object?
• No charge is transferred
• These objects are called insulators.
• Metals are generally good conductors whereas most other
materials are insulators.
– A 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 tightly bound electrons!
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
34
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
object still move within the metal toward the charged
object leaving the opposite end of the object positively
charged.
• The charges have been “induced” in the opposite ends of the
object.
Tuesday, June 5, 2012
PHYS 1444-001, Dr. Andrew Brandt
35
Induced Charge
ground
• We can induce a net charge on a metal object by
connecting a wire to 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
rod
– Positive charges in the neutral rod will be attracted by the
negatively charged metal.
– The negative charges in the neutral metal will gather 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
measuring charge – How?
PHYS 1444-04 Dr. Andrew Brandt
36
Coulomb’s Law
• Charges exert force on each other. What factors affect the
magnitude of this force?
• Charles Coulomb figured this out in 1780’s.
• Coulomb found that the electrical force is
– Proportional to the product of the two charges
• If one of the charges is doubled, the force doubles.
• If both of the charges are doubled, 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 this into a formula?
Wednesday, Aug. 31,
2011
PHYS 1444-04 Dr. Andrew Brandt
37
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 two charges have the same sign: forces are directed away from each other.
– If two charges are of opposite sign: forces are directed toward each other.
• Coulomb’s Law is accurate to 1 part in 1016.
• Unit of charge is called Coulomb, C, in SI.
• The value of the proportionality constant, k, in SI
units is k  8.988  109 N  m2 C 2
• Thus, if two 1C charges were placed 1m apart
9N. 1444-04 Dr. Andrew Brandt
Wednesday,
Aug.would
31,
PHYS
the
force
be
9x10
2011
38
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: Charge, fundamental property of matter
– Gravitational Force: Mass, fundamental property 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 different?
– Gravitational force is always attractive.
– Electric force depends on the sign of the two charges.
– Magnitude
Wednesday, Aug. 31,
2011
PHYS 1444-04 Dr. Andrew Brandt
39
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 always occurs 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.
Wednesday, Aug. 31,
2011
PHYS 1444-04 Dr. Andrew Brandt
40
Example 21 – 1
• Electric force on electron due to proton. Determine the
magnitude of the electric force on the electron in 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 = 0.53 x10-10 m. (0.5 Angstrom)
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?
Wednesday, Aug. 31,
2011
10
19
C

2
Towards each other…
PHYS 1444-04 Dr. Andrew Brandt
41
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!
Is there any difference?
The direction.
What is the direction?
Opposite to each other!
What is this law?
Newton’s third law, the law of action and reaction
Wednesday, Aug. 31,
2011
PHYS 1444-04 Dr. Andrew Brandt
42
Solving Problems
•
•
•
•
•
•
•
•
•
Read and re-read problems carefully
Draw a diagram using arrows to represent vectors
Choose a convenient coordinate system
Note the known and unknown quantities
Write down the relevant relationships
Do an approximate calculation
Solve, substituting numbers only at the end
Keep track of units
Consider if answer is reasonable
Wednesday, Aug. 31,
2011
PHYS 1444-04 Dr. Andrew Brandt
43
Vector Problems
• Calculate magnitude of vectors
• Split vectors into x and y components
and add these separately, using
diagram to help determine sign
• Calculate magnitude of resultant
|F|=(Fx2+Fy2)
• Use = tan-1(Fy/Fx) to get angle
Example on board
Wednesday, Aug. 31,
2011
PHYS 1444-04 Dr. Andrew Brandt
44
Announcements
• Read Ch. 21 before next class
• Enroll in Mastering Physics and do first “welcome”
assignment
• Read Book, Do HW, Go to Lab, Learn Physics
• Good grade will follow
Wednesday, Aug. 31,
2011
PHYS 1444-04 Dr. Andrew Brandt
45