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PHYS 241D Electricity & Optics
• Physics Department Home page: http://www.physics.purdue.edu/
• Course Home page: http://www.physics.purdue.edu/phys241/
• CHIP Home page: http://chip.physics.purdue.edu/public/241/spring2016/
• Piazza: https://piazza.com/purdue/spring2016/phys241/home
• Room 144 - Undergraduate office
• Room 11 - Help center
• Room 290 - Physics Library
Course Home page:
http://www.physics.purdue.edu/phys241/
Calendar &
Syllabus are
under this link.
Lecture notes
will posted here.
Calendar/Schedule (posted under Course Information)
*Read the assigned
Chapter sections
prior to watching
the lecture.
*Note Exam Dates
*Homework is usually
due on Mondays at
11:59 PM.
Homework is done
through CHIP.
*Lecture quizzes are due
on Friday.
*Recitation quizzes are
due on Mondays.
CHIP Home page:
http://chip.physics.purdue.edu/public/241/spring2016/
Syllabus
*Register your I-clicker on CHIP.
*Always bring your I-clicker to class.
*5% of your point total is based on
lecture quizzes.
CHIP: http://chip.physics.purdue.edu/public/241/spring2016/
Syllabus
Questions about grades, grade
checks, absences, etc… please see
Prof. Pyrak-Nolte
Send an e-mail to make an in-person appointment or an
audio appointment by Skype
Online Forum
We will use Piazza for class discussions to assist you in getting
help fast and efficiently from your classmates and the teaching
assistants. Rather than emailing questions to the teaching staff,
you are encouraged to post your questions on Piazza:
You can sign up for a Piazza account and enroll in our class
page at:
https://piazza.com/purdue/spring2016/phys241/home
You can also use Piazza to set-up study groups with other
students in PHYS 241 & PHYS 241D
To report an emergency, call 911. To obtain updates regarding an ongoing
emergency, sign up for Purdue Alert text messages, view www.purdue.edu/ea.
There are nearly 300 Emergency Telephones outdoors across campus and in
parking garages that connect directly to the PUPD. If you feel threatened or need
help, push the button and you will be connected immediately.
If we hear a fire alarm during class we will immediately suspend class, evacuate
the building, and proceed outdoors. Do not use the elevator.
If we are notified during class of a Shelter in Place requirement for a tornado
warning, we will suspend class and shelter in [the basement].
If we are notified during class of a Shelter in Place requirement for a hazardous
materials release, or a civil disturbance, including a shooting or other use of
weapons, we will suspend class and shelter in the classroom, shutting the door and
turning off the lights.
Please review the Emergency Preparedness website for additional information.
http://www.purdue.edu/ehps/emergency_preparedness/index.html
EMERGENCY PREPAREDNESS – A MESSAGE FROM PURDUE
Electric & Magnetic Fields
Electric and magnetic fields manifest their existence
through interactions with matter.
Maxwell’s Equations
Lorentz Force
o
div E E
0div B B
o o
Ecurl B B J
t
B
curl E Et
enclosed
oS
QE dA
0S
B dA
C S
BE dl dA
t
o o o
C S
EB dl I dA
t
Differential Form Integral Form
F qE qv B
James Clerk Maxwell
(1831–1879)
Lecture 1 Electric Charges & Coulomb’s Law
www.ehow.com/how_2180464_reduce-
static-cling.html
http://www.diyhappy.com/wp-
content/images/Lightning.bmp
http://andreacarlisle.files.wordp
ress.com/2012/02/static-
cling_dogs.jpg
Electric Charge
Electric charge is an intrinsic characteristic of the fundamental
particles that make up objects.
+
Positive Charge Negative Charge
•Electrically neutral: object contains equal amounts of
positive and negative charges
•Net charge: imbalance in charge
Electric Charge
Net charge of a system:
algebraic sum of all the charges
Law: Conservation of charge
The net charge of a closed system never changes
Electric Charge
Electric charge is quantized
•Elementary charge:
q ne, n 1,2,3,.....
e = 1.60602176462(63) x 10–19 C
Coulomb (C): one coulomb is the amount of charge that is
transferred through the cross section of a wire in 1 second
when there is a current of 1 ampere in the wire.
$ = n
http://scrapetv.com/News/News%20Pages/B
usiness/images/us%20penny.jpg
Charge of Particles Electron
Positron
Proton
Anti-Proton
Neutron
Photon
Up Quark
Down Quark
0
Particles Charge
Nucleus charge= +Ze, atom with Z electrons is neutral.
e
e
e
e
2
3e
1
3e
0
Proton charge: |e+ | = 1.60 x 10–19 C
Electron charge: |e- | = 1.60 x 10–19 C
Conductors versus Insulators
• Conductors: material in which electric charges can move around “freely.
• Insulators: material in which electric charges are “frozen” in place.
• Semi-conductor: material in which electric charges can move around but not as freely as in conductors.
• Super-conductor: no resistance to the movement of charge.
Interaction of Charges: Insulators
•Insulators: material in which electric charges are “frozen” in place.
Interaction of Charges: Insulators
Force of Repulsion Force of Attraction
Charges with opposite
electrical signs attract each
other.
Charges with the same
electrical sign repel each
other
Mobility of Charge
• Conductors: material in which electric charges can move around “freely.”
• Negatively charged plastic rod
will attract either end of the
electrically isolated copper rod
• Reason: charges in copper rod
can redistribute themselves.
Charging by Induction
1. Bring a charged rod close to conductor.
2. Ground the conductor.
3. Break connection to ground, keeping the
charged rod in place
4. Remove the rod. The sphere is charged.
Coulomb’s Law of Electro-static Force
q1 q2
r
The electro-static force of attraction/repulsion has a
magnitude:
F kq1 q2
r2
Coulomb’s Law
k 1
4o 8.99x109Nm2 /C2
where:
and the permittivity constant is o 8.55x1012C2 / Nm2
Charles-Augustin de
Coulomb
(1736 - 1806)
Coulomb’s Law of Electro-static Force
*Each particle exerts a force of this magnitude on the other
particle.
*The two forces form an action-reaction pair.
1 2
2
1ˆ
4 o
Q QF r
r
Force repulsive
1
+
+
2
r F12
Force attractive
+
-
2
r
F12
1
Force by “1” on “2”
Coulomb’s Law of Electro-static Force
Force exerted by q1 on q2 at a distance r12
1 212 1,22
1,2
ˆ kq q
F rr
12 1,2
12 1,2
Same sign charges: is in the direction of .
Opposite sign charges: is in the direction opposite to .
F r
F r
q1, q2 in coulombs (C)
r12 in meters (m)
F12 in newtons (N)
12 F
Coulomb’s Law Analogous to Newton’s Equation of
Gravitation
F kq1 q2
r2F G
m1m2
r2
* k electro-static constant
* Inverse Square Law
* Charge
*Attractive/repulsive
depending on sign of
charges
*Two kinds of charges
*Dominates on small scale
* G gravitational constant
* Inverse Square Law
* Mass
*Always attractive
*One kind of mass
*Dominates on large scales
DIFFERS
Analogous
Quiz 1. January 11, 2016
Two charges q = + 1 µC and Q = +10 µC are placed near each other as
shown below. Which diagram best depicts the electrostatic forces
acting on the charges?
+1 µC +10 µC
A
B
C
Quiz 1. January 11, 2016 Consider the two cases shown below. In both cases, a central
charge q has two charges of equal magnitude at equal distances
above and below it. In Case 1, the signs of the two outer
charges are opposite, and in Case 2 they are both positive. You
are not told the sign of the charge in the center.
Case 1 Case 2
+Q +Q
-Q +Q
q q
In which Case is the magnitude of
the net force on the center charge
bigger:
A.Case 1
B.Case 2
C.They are the same.
D.The answer depends on the sign of
the charge q in the center.
Problem Solving Strategies:
• Draw a clear FORCE diagram
• Use consistent units (meter, Coulomb, Newton)
• Remember that the force is a vector
• Look for (possible) symmetry
Principle of Superposition • When several point charges are put together, the total force on
any one charge is the vector sum of the each of the separate
forces acting on that charge.
F F21y F31y 2F21y
F 2 kQ1Q2
r2cos 300
F
2 9 109 N m2
C 2 (106C)2 0.866
1m 2
F 15.59 103N
F
F21
• Exercise:
Q2
Determine force on Q1
Q1=Q2=Q3=1C Q3
R=1m
600
Q1
y
x Determine force on Q1
F31
Electro-Static Force versus Newton’s Force of
Gravitational Attraction
Given such strong electrical interactions, atoms tend to remain uncharged. Matter prefers to be neutral.
Forces we experience, if not gravitational, are electrical in nature (even
though the net charge may be zero).
2
e
grav2
2
el
mF
e F
r
mG
rk
p
Fel
Fgrav
k
G
e2 / r2
memp / r2 1.35 1020 kg2
C2
(1.6 1019C)2
(1.7 1027Kg)(9.11031Kg)
Fel
Fgrav
2.3 1039 Fel 8.2 10-8N Fgrav 3.6 1047 N
Fel between the proton and the electron in a hydrogen atom in the ground state. From the Bohr model r=0.53 x 10-10 m.
Quiz 1. January 11, 2016
The nucleus of a Helium atom has a charge equal to
twice the proton’s charge. Let FN denote the magnitude
of the force the Helium nucleus exerts on one of the
electrons in a Helium atom, and Fe denote the
magnitude of the force one electron in the Helium atom
exerts on the Helium nucleus. Which of the following
statements concerning the magnitudes of FN and Fe is
true?
(A) FN < Fe
(B) FN = Fe
(C) FN > Fe
Quiz 1. January 11, 2016
Two charges q = + 1 µC and Q = +10 µC are placed near each other as
shown below. Which diagram best depicts the electrostatic forces
acting the charges?
+1 µC +10 µC
A
B
C