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7/18/2019 PHYS 241 Lecture 1
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PHYS 241D Electricity & Optics
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Physics Department Home page: http://www.physics.purdue.edu/
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Course Home page: http://www.physics.purdue.edu/phys241D/
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CHIP Home page: http://chip.physics.purdue.edu/public/241D/spring2015/
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Piazza: https://piazza.com/purdue/spring2015/phys241/home
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Room 144 - Undergraduate office
•
Room 11 - Help center
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Room 290 - Physics Library
Course Home page:
http://www.physics.purdue.edu/phys241D/
Calendar & Syllabus are
under this link.
Calendar/Schedule (posted under Course Information)
*Read the assigned
Chapter sections
prior to watching thelecture.
*Note Exam Dates
*Homework is due on
Mondays at 11:59 PM.
Homework is donethrough CHIP.
*Lecture quizzes are due
on Friday.
*Recitation quizzes are
due on Mondays.
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Homework: http://chip.physics.purdue.edu/public/241D/spring2014/
*Check your schedule for the time of your online recitation. See PHYS241Dhomepage for the link t o the online recitation classroom using WebEx
CHIP Home page: http://chip.physics.purdue.edu/public/241D/spring2014/
Homework: http://chip.physics.purdue.edu/public/241D/spring2014/
Homework: http://chip.physics.purdue.edu/public/241D/spring2014/
*Answer Survey before due date
& receive 10 homework bonuspoints
*Note Due
Dates…always
check as thedates may
change due to
unforeseen
circumstances
Homework: http://chip.physics.purdue.edu/public/241D/spring2014/
*Note: Recitation Quiz 00 takes 30 minutes. Please start prior to 11:00 PM Jan
16, 2015 to have the complete 30 minutes. Remember: Once you open a
quiz and close it, you cannot re-open it.
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Course Home page: http://www.physics.purdue.edu/phys241D/
Link to lecture
notes. Fill in
notes as youwatch the
lecture on
Boilercast
Online Recitations
Link for “live” onlinerecitations. Meetingnumber & password willbe e-mailed to you.Recitations will also berecorded for later viewing.
http://www.itap.purdue.edu/learning/tools/webex/
Read the Syllabus for additional details 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/spring2015/phys241/
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Additional Resource:
Short YouTube Videos onselected topics.
Electric & Magnetic Fields
Electric and magnetic fields manifest their existencethrough interactions with matter.
Maxwell’s Equations
Lorentz Forcediv
!
E( ) =
!
! "!
E =
#
$ o
div!
B( ) =
!
! "!
B = 0
curl!
B( ) =
!
! " !
B = µ o
!
J + # o
$ !
E
$ t
%
& '
(
) *
curl!
E( ) =
!
! "!
E = #$ !
B
$ t
!
E !d !
A =
Qenclosed
" oS
#
!
B !d !
A = 0
S
"
!
E ! d !
l = "C
# $
!
B
$ t ! d
!
A
S
#
!
B !d !
l = "C
# µ o I + µ
o$ o
%
E
% t ! d
!
A
S
#
Differential Form Integral Form
!
F = q!
E + q!
v !!
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
Electric Charge
Electric charge is an intrinsic characteristic of the fundamental
particles that make up objects.
+
Positive Charge Negative Charge
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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
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Elementary charge:
e = 1.60602176462(63) x 10 –19 C
Coulomb (C): one coulomb is the amount of charge that istransferred through the cross section of a wire in 1 secondwhen there is a current of 1 ampere in the wire.
$ = n
http://scrapetv.com/News/News%20Pages/Business/images/us%20penny.jpg
Charge of Particles
+ Ze
neutral atom
electron
orbits
nucleus
e –
e –
e –
Electron
Positron
Proton
Anti-Proton
Neutron
Photon
0
Particles Charge
Nucleus charge= +Ze, atom with Z electrons is neutral.
e!
e!
e+
e+
0
Proton charge: |e+ | = 1.60 x 10 –19 C
Electron charge: |e- | = 1.60 x 10 –19 C
Interaction of Charges
Charged objects interact by exerting forces on one another.
DEMO: Pith Balls
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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 canmove around but not as freely as in conductors.
• Super-conductor: no resistance to the movement ofcharge.
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 movearound “freely.
• Negatively charged plastic rod
will attract either end of the
electrically isolated copper rod
• Reason: charges in copper rod
can redistribute themselves.
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Conductors versus Insulators
• Demo 5A-04: Charges are more readily
transferred by conductors
Mobility of Charge
• Demo: Pie Tins
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.
Charge Induction
•
Demo: Chimes
Conducting
thread
Insulating
thread
Grounded
Charged
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Coulomb’s Law of Electro-static Force
q1 q2
r
The electro-static force of attraction/repulsion has amagnitude:
Coulomb’s Law
k =1
4!" o
= 8.99 x109 Nm
2/C
2
where:
and the permittivity constant is ! o = 8.55 x10
"12C
2/ Nm
2
Charles-Augustin deCoulomb
(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.
!
F=
1
4!" o
Q1Q
2
r2 ˆr
1
+
+
2 +
-
2
1
Coulomb’s Law of Electro-static Force
Force exerted by q1 on q
2 at a distance r
12
!
F 12 =
kq1q
2
r1,2
2 r̂1,2
q1, q2 in coulombs (C)
r 12
in meters (m)
F 12
in newtons (N)
!
F 12
Coulomb’s Law Analogous to Newton’s Equation
of Gravitation
F = k q1 q
2
r2F = G
m1m
2
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
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Electro-Static Force versus Newton’s Force ofGravitational Attraction
DEMO: 2 x 4
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.
•
Exercise:
Q2
Determine force on Q1
Q1=Q2=Q3=1!C Q3
R=1m
600
Q1
y
xDetermine force on Q1