PHYS 241 Lecture 1

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

•

Room 144 - Undergraduate office

•

Room 11 - Help center

•

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.

7/18/2019 PHYS 241 Lecture 1


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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/



*Answer Survey before due date

& receive 10 homework bonuspoints

*Note Due

Dates…always

check as thedates may

change due to

unforeseen

circumstances


*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.

7/18/2019 PHYS 241 Lecture 1


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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

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Read the Syllabus for additional details Online Forum

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You can sign up for a Piazza account and enroll in our class

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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

7/18/2019 PHYS 241 Lecture 1


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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)


*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


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

PHYS 241 Lecture 1

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