Transcript Slide 1

PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
PHYSICS 272
Electric & Magnetic Interactions
 You Are in This Section
Section 1 MW 8:30-9:20AM
Prof. Michael Manfra
[email protected]
Room:84, Phone:43016
Section 2 MW 9:30-10:20AM
Prof. Yong Chen
[email protected]
The two sections cover the same material
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 1
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Course Content
This course deals with electric and magnetic interactions,
which are central to the structure of matter, to chemical and
biological phenomena, and to the design and operation of
most modern technology [foundational to all engineering]
The main goal of this course is to have you engage in a
process central to science: the attempt to model a broad
range of physical phenomena using a small set of powerful
fundamental principles. The specific focus of the course is an
introduction to field theory, in terms of the classical theory of
electricity and magnetism (E&M). The course also
emphasizes the atomic structure of matter, especially the role
of electrons and protons in matter.
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 2
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Schedule
• Lectures --- One of the follow sections
(Sec. 1): Monday, Wednesday 8:30 - 9:20AM (50 minutes)
– Lecture Room: PHYS 112
– Instructor: Prof. Michael Manfra
– Office hours: by appointment
– Office: PHYS 84 , Phone: (49)-43016
– Email: [email protected] (please use subject: PHYS 272)
(Sec. 2): Monday, Wednesday 8:30 - 9:20AM (50 minutes)
– Lecture Room: PHYS 112
– Instructor: Prof. Yong Chen
– Office hours: by appointment
– Office: PHYS 74 , Phone: (49)-40947
– Email: [email protected] (please use subject: PHYS 272)
• Teaching Assistants (Rec/Lab): Jonathan Nistor, David Blasing,
Mike Fink, John Doyle, Mark Palenik, Zachary Wolff
• Course information:
– http://www.physics.purdue.edu/academic_programs/courses/phys272/
– Undergraduate Office - PHYS 144
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 3
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Textbook
The textbook is Matter & Interactions,
vol II: Electric & Magnetic Interactions
by R. Chabay & B. Sherwood (John
Wiley & Sons 2011). We will cover
almost all of the topics in this volume.
See the table of contents at the front of
the book (which also includes the
contents of Volume I).
Make sure it is the Third Edition. The new book comes with a
free coupon for WebAssign, the on-line homework service.
Follow the instructions and get yourself registered.
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 4
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
General Information
Room PHYS 144: Undergraduate office
Room PHYS 12: Help center
Room PHYS 290: Physics Library
We will use WebAssign for homework and lab
assignments.
You will be able to access your scores in CHIP.
See “Important Links” on course web page for
details!
For questions concerning WebAssign contact:
V.K. Saxena: Office: PHYS 176, Phone: 49575
Email: [email protected]
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 5
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Activities and Responsibilities
• In-class activities and responsibilities
– You are responsible for attending all classes, and attendance will
count toward your grade.
– Bring the textbook and a scientific calculator to class.
– If you miss class, it is your responsibility to find out what you missed.
Lectures slides will be available shortly after lecture concludes.
• Recitations and Lab Sessions
• Homework
– Homework and lab assignments will be posted on the web. See
WebAssign (and Calendar section) for due dates.
• Outside class
– Study assigned textbook sections.
– An assignment to study sections of the textbook means:
• Read the assigned textbook sections thoughtfully (try “self-retrieving”).
• Do the "stop and think" activities.
• Write brief solutions to the in-line "exercises" and keep them in a
notebook.
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 6
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Quizzes, Exams, Grades
• Clicker Questions in Lecture:
– Short multiple choice questions will be posed in lecture. The purpose is to assess your
understanding. It will also be used to check attendance. We will start counting clicker
questions towards your grade at lecture #5.
– You have to purchase an iClicker ( http://www.iclicker.com ) from the bookstore.
– You must register your clicker ID in CHIP!!!!
• Exams:
– There will be two 1.5-hour exams and a 2-hour final exam. All exams are closed-book, but
relevant formulas and constants will be provided.
• Grades:
– The final grade will be determined on the following basis (Course Total = 700 points):
• 200 points - final exam
• 100 points each - two 1.5-hour exams (see calendar)
• 75 points - WebAssign homework
• 100 points – Labs
• 25 points - Clicker Questions & Attendance
• 50 points – Weekly Quizzes
• 50 points – Recitation Problems
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 7
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
This Week
• Study chapter 13
• Lab will start this Wed, Thurs, Friday: PreCourse Assessment
• Do Homework in WebAssign
Announcement
Lab Manuals no longer available in Union/BoilerCopyMaker
Please print your copy BEFORE coming to Lab!
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 8
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Electric and Magnetic Fields
Electric and magnetic fields manifest their existence through
interactions with matter
Maxwell equations:
  

div(E )    E 
0
 

div(B)    B  0
B
curl(E)    E  t

 


E 
curl(B)    B  0  J   0


t


Lorentz force:


 
F  qE  qv  B
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 12
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Point Charges
• Two types: positive and negative
• Like charges: repel
• Opposite charges: attract
• Charge is quantized in units of e
Millikan’s oil drop experiment (1910-1913)
“Fractional” quantized charge (quarks, FQHE…)
[not in everyday life]
• Point charge: Size is small compared to the distance between it and
other objects of interest
• Electric charge is an intrinsic property of the fundamental particles
that everything is made of
• Universe’s Net charge is conserved
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 13
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
The Coulomb Force Law

1 Q1Q2
F F
2
4 0 r
"The magnitude of the electrostatic force between two
point charges is directly proportional to the
magnitudes of each charge and inversely proportional
to the square of the distance between the charges."
Charles-Augustin de Coulomb
Q1
Q2
F
(1736 - 1806)
F
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 14
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
The Coulomb Force Law
1 Q1Q2
ˆ
F
r
 = permittivity constant of
2
vacuum (air is close)
4 0 r
0
r
+
+
2
F21
Force on “2” by “1”
1
Force repulsive
+
r
-
F21
2
1
Force attractive
• The force exerted by one point charge on another acts along line
joining the charges.
• The force is repulsive if the charges have the same sign and
attractive if the charges have opposite signs.
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 15
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Units and Constants

1
SI units of electric charge: Coulomb, C
F F
4 0
Constants:
1/40 = 9x109 N.m2/C2
0 = 8.85x10-12 C2/N.m2 permittivity constant of vacuum
e = 1.602x10-19 C (“unit charge’)
1 C = 6.24x1018 elementary charges
Particle Charge
electron
-e
positron
+e
proton
+e
antiproton
-e
neutron
0
photon
0
up quark
+(2/3)e
down quark
-(1/3)e
Q1Q2
r2
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 16
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Structure of Atom
Matter consists of atoms
1 cm3 : ~1024 atoms
Nucleus:
~104 times smaller than electron cloud,
~104 times heavier than electron.
1Å=0.1nm=10-10m
Example: nucleus of the iron atom
Size: ~10–15 m, mass: ~10-25 kg
Nucleus charge = +Ze, atom with Z electrons is neutral.
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 17
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
The Concept of Electric Field
Accelerates at 9.8 m/s2 – why?
Accelerates at 1011 m/s2 – why?
There are many possible
configurations of charges
to produce the observed
effect.
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 18
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Electric Field
There is something in space
waiting for a charged particle to
interact with it!
This virtual force is called
electric field.
An electric field created by charge is present throughout
space at all times, whether or not there is another charge
around to feel its effect.
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 19
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Definition of Electric Field
q1q2
F
4 0 r 2
1
 1 q1 

F  q2 
2 
 4 0 r 


F2  q2 E1


E1  F2 / q2
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 20
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Electric Field
 
E  F /q
If our probe charge is positive or
negative
F due to given E will point in correct
direction.
 
E  E x, y, z, t 
Electric field has units of Newtons per Coulomb:
[N/C]
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 21
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
The Electric Field of a Point Charge
 1 q1 

F  q2 
2 
 4 0 r 


F2  q2 E1
q1
E1 
4 0 r 2
1
+
Including direction:

E1 
1
q1
rˆ
2
4 0 r
-
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 22
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Example Problem
A particle with charge +2 nC (1 nanoCoulomb=10-9 C) is located
at the origin. What is the electric field due to this particle at a
location <-0.2,-0.2,-0.2> m?

Solution:
1 q1
ˆ
E

r
1
2
1. Distance and direction:
4 0 r

r

r  observed _ location - source _ location

r  -0.2, -0.2, -0.2 - 0, 0, 0  -0.2, -0.2, -0.2

r 
-0.2 2  -0.2 2  -0.2 2
 0.35 m

-0.2, -0.2, -0.2
r
 -0.57, -0.57, -0.57
rˆ   
r
0.35
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 23
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Example Problem

E1 
2. The magnitude of the electric field:
1
q1
rˆ
2
4 0 r
2
-9


q 
Nm
2

10
C
N
9

  147
E
  9  10
2
2 
2
2 
4 0 r
C  0.35 m 
C

1
3. The electric field in vector form:

N

E  Erˆ  147  - 0.57,-0.57,-0.57
C


N
E  - 84,-84,-84
C
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 24
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
The Physical Concept of ‘Field’
Field: physical quantity, can be scalar or vector
Examples:
Temperature T(x,y,z,t) --- scale
Air flow, gravitational field --- vector
m


F  mg


F  qE
q
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 25
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Forces due to an Electric Field
Example: The electric field at a particular location
is <-300,0,0> N/C. What force would an electron experience
if it were placed in this location?
Y
E
e
F
X


Solution: F  -eE  -1.6  10-19 C - 300,0,0 N/C

F  4.8  10-17 ,0,0 N
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 26
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Re-Cap (EMI 14.1-14.3)
• Course elements: lecture, recitation, lab,
WebAssign…
• Coulomb’s law for electric force
• Point charges and unit of charge
• Electric force  electric field
Next time (EMI 14.4-14.8)
• Superposition of Electric field due to multiple
charges
• Electric dipole
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 27
PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions
http://www.physics.purdue.edu/academic_programs/courses/phys272/
Food for Thought: “Coulomb” Blockade
Moore’s law
Small transistors: Single electron charge matters!
To read more:
Marc Kastner: “Artificial Atoms”, Physics Today, Jan. 1993, pp24
“Coulomb blockade lab”: http://nanohub.org/resources/4231
Fall 2010 Prof. Yong Chen ([email protected]) Prof. Michael Manfra ([email protected]) Lecture 1 Slide 28