1. Physics 241: Electricity and Optics
1st Lecturer : Prof. Yeong Kim nd Lecturer Prof. Rolf Scharenberg
Office: Room 258, Physics building Office: Room 249, Physics Building
Phone: Phone:
Lecturer in Charge: Prof. Laura Pyrak-Nolte Administrator: Dr V. K. Saxena
Office: Room 176, Physics Building Office: Room 176, Physics Building
Phone: Phone:
Office: Room 166, Physics Building
Phone:
Office Hours: M 11:30, or by appointment
Office Hours: Kim, Scharenberg, and Saxena by appointment

2. Physics 241 Electricity and Optics
TEXTBOOK
Physics for Scientists and Engineers, 6th edition, Volume 2
Paul A. Tipler and Gene Mosca (W. H. Freeman and company)
I-CLICKER
Audience response device, ISBN
Publishers Bedford, Freeman and Worth
To activate your I-Clicker you will need to place the ID-code
from the device into CHIPS the first time you login. You should
do this as soon as possible as the I-Clicker be used during the first
week of class, both in lecture and recitation. (see syllabus)
CLICKER QUESTIONS IN LECTURE
There is one clicker point for logging in at the lecture. There will a
clicker graded question about the assigned reading material
at the beginning of each lecture, followed by an ungraded warmup
quiz and finally a graded quiz question. (total 3 points possible)
PHYSICS 241 WEB SITE: .

3. An Old (and Fundamental
An Old (and Fundamental!) Question: What is the Structure of Matter in the Universe?

4. Size Scales in the Universe
Ancient Man ~1m
Universe
Scale ~ 1026 m
Iron
Wood
Gravitation
Leptons
Quarks
Gluons
Basics Constituents
Scale ~ m
Electromagnetism
Nuclei ~ m
Strong Nuclear Force
Atoms

5. Reading Quiz 1
An electron with charge -e annihilates with an anti-electron +e (positron)
and produces two gamma rays. Does this violate charge conservation ?
(A) yes, charge is destroyed.
(B) No, net charge is conserved.
(C) No, gamma rays have charge.
(D) Yes, physical laws work on the large scale not at the individual quantum scale.

6. Concept of Charge -- Charging by rubbing

7. DEMO #5A01
STATIC ELECTRICITY

8. Charging by induction
polarization by induction
grounding

9. friction can cause electrons to move from one object to another.

10. 2 x 4 ELECTROSCOPE
DEMO # 5A-06

11. Quantization of Charge
Fundamental unit: elementary charge e
An electron carries a charge of –e ; a proton carries a charge of +e
It is typically the electrons that move
between objects.
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.

12. Conductor vs. Insulator
Conductors: material in which electric charges can move around “freely”
Metals, tap water, human body, …
Insulators: material in which electric charges are “frozen” in place
Air, glass, plastic, …
Semi-conductor: material in which electric charges can move around but not as freely as in conductors
Silicon, germanium, …
Cu / m3
Ge / m3

13. Conservation of Charge
The net electric charge is conserved in any physical process. But …
Charge can be transferred from one object to another.
Individual charges can also, in fact, be “destroyed” or “created”, but not net charges
( annihilation)
( pair production)

14. POPULAR SCIENCE ATOM SKETCH

15. Coulomb’s Law
Charges with the same sign repel each other, and charges with opposite signs attract each other.
The electrostatic force between two particles is proportional to the amount of electric charge that each possesses and is inversely proportional to the distance between the two squared. q1 q2 r
by 1 on 2
1,2
1,2
1,2
Coulomb constant:
where e0 is called the permittivity constant.

16. How strong are Coulomb forces?
Electron and proton in a hydrogen atom
Compare electric and gravitational forces
electron and proton
me = 9.11x10-31 kg,
mp =1.67x10-27 kg

17. A Human weighs 120 lb, which of the
Warm-up Quiz Question 2
A Human weighs 120 lb, which of the
following statements are correct?
A large fraction of the weight come from the attraction force between the electric charges on human body and earth.
All the weight comes the attraction force between the electric charges on the human body and the earth.
All the weight come from the gravitational forces. The electric forces are negligible.

18. Principle of Superpositionq1 q2 q3
F13
F12 F1
Add by components or
Magnitude and direction separately by using trigonometry

19. Warm-up Quiz 3
One known charge Q1 = Q > 0 and the other unknown positive charge Q2 > 0 are held fixed at a separation d = R as shown.
Another (non-zero) charge Q3 is introduced somewhere along the line connecting Q1 and Q2.
Which of the following statements is true?
A) The force on Q3 can be zero only if Q3 is placed to the left of Q1.
B) The force on Q3 can be zero only if Q3 is placed between Q1 and Q2.
C) The answer to above depends on the sign of Q3.
D) The answer to above depends on the magnitudes of Q1 and Q2 .
E) The force on Q3 can never be zero, no matter what the (non-zero!) charge Q3 is.

20. Physics 241 – 10:30 Quiz 3 – August 23, 2011
Two point charges are separated by distance d as shown. Where can you put a third charge of
1 C so that there is no net electric force acting on it? (Take Q > 0.)
to the right of charge Q
to the left of charge 2Q
between the two charges
some other place
nowhere 2Q Q d
e = 1.6 x C
k = 8.99 x 109 Nm2/C2

21. Physics 241 – 11:30 Quiz 3 – August 23, 2011
Two point charges are separated by distance d as shown. Where can you put a third charge of
+1 C so that there is no net electric force acting on it? (Take Q > 0.)
to the right of charge –Q
to the left of charge 2Q
C) between the two charges
D) some other place
E) nowhere 2Q
- Q d
e = 1.6 x10-19 C
k = 8.99 x 109 Nm2/C2

22. Physics 241 – 11:30 Quiz 3 – Jan. 11, 2011
Two point charges are separated by distance d as shown. Where can you put a third charge of
+1 C so that there is no net electric force acting on it? (Take Q > 0.)
to the right of charge -2Q
to the left of charge Q
C) between the two charges
D) some other place
E) nowhere Q
- 2Q d
e = 1.6 x C
k = 8.99 x 109 Nm2/C2