Physics 241: Electricity and Optics 1st Lecturer : Prof. Yeong Kim 2nd Lecturer Prof. Rolf Scharenberg Office: Room 258, Physics building Office: Room 249, Physics Building Phone: 494-3042 Phone: 494-8748 Email: yekim@purdue.edu Email: schrnbrg@purdue.edu Lecturer in Charge: Prof. Laura Pyrak-Nolte Administrator: Dr V. K. Saxena Office: Room 176, Physics Building Office: Room 176, Physics Building Phone: 494-9575 Phone: 494-9575 Office: Room 166, Physics Building Email: saxena@physics.purdue.edu Phone: 494-3005 Email: ljpn@purdue.edu Office Hours: M 11:30, or by appointment Office Hours: Kim, Scharenberg, and Saxena by appointment

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 0-7167-7939-0 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: http://www.physics.purdue.edu/physics241 .

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

Size Scales in the Universe Ancient Man ~1m Universe Scale ~ 1026 m Iron Wood Gravitation Leptons Quarks Gluons Basics Constituents Scale ~ 10-10 m Electromagnetism Nuclei ~ 10-15 m Strong Nuclear Force Atoms

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.

Concept of Charge -- Charging by rubbing

DEMO #5A01 STATIC ELECTRICITY

Charging by induction polarization by induction grounding

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

2 x 4 ELECTROSCOPE DEMO # 5A-06

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.

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 1029 / m3 Ge 1019 / m3

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)

POPULAR SCIENCE ATOM SKETCH

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.

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

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.

Principle of Superposition q1 q2 q3 F13 F12 F1 Add by components or Magnitude and direction separately by using trigonometry

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.

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 10-19 C k = 8.99 x 109 Nm2/C2

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

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 10-19 C k = 8.99 x 109 Nm2/C2