Lecture 1-1 Physics 241: Electricity and Optics Lecturer in charge: Prof. X. Wei Lecture 9:30 am-10:30 am Office: Room 246, Physics building Phone: Lecturer: Prof. R. P. Scharenberg CHIP Administrator: Dr. V. K. Saxena Lecture: 10:30 am-11:20 am Office: Room 176, Physics Building Lecture: 11:30 am-12:20 am Phone: Office: Room 245, Physics Building Phone: Office Hours for Saxena, Scharenberg, Wei by appointment

Lecture 1-2 Physics 241 Electricity and Optics TEXTBOOK Physics for Scientists and Engineers, 6 th 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 REVIEW QUESTION There will a clicker graded question about the assigned reading material at the beginning of each lecture. PHYSICS 241 WEB SITE:

Lecture 1-3 An Old (and Fundamental!) Question: What is the Structure of Matter in the Universe?

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

Lecture 1-5 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.

Lecture 1-6 Concept of Charge -- Charging by rubbing

Lecture 1-7 Charging by induction grounding polarization by induction

Lecture 1-8 friction can cause electrons to move from one object to another.

Lecture x 4 ELECTROSCOPE

Lecture 1-10 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.

Lecture 1-11 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 / m 3 Ge / m 3

Lecture 1-12 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)

Lecture 1-13 POPULAR SCIENCE ATOM

Lecture 1-14 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. q1q1 q2q2 r 1,2 where   is called the permittivity constant. Coulomb constant: 1,2 by 1 on 2

Lecture 1-15 How strong are Coulomb forces? Electron and proton in a hydrogen atom Compare electric and gravitational forces electron and proton m e = 9.11x kg, m p =1.67x kg

Lecture 1-16 Quiz Question 2 A Human weighs 120 lb, which of the following statements are correct? a)A large fraction of the weight come from the attraction force between the electric charges on human body and earth. b)All the weight comes the attraction force between the electric charges on the human body and the earth. c)All the weight come from the gravitational forces. The electric forces are negligible.

Lecture 1-17 Principle of Superposition q1q1 q2q2 q3q3 F 13 F 12 F1F1 Add by components or Magnitude and direction separately by using trigonometry

Lecture 1-18 Warm-up Quiz 3 One known charge Q 1 = Q > 0 and the other unknown positive charge Q 2 > 0 are held fixed at a separation d = R as shown. Another (non-zero) charge Q 3 is introduced somewhere along the line connecting Q 1 and Q 2. –Which of the following statements is true? A) The force on Q 3 can be zero only if Q 3 is placed to the left of Q 1. E) The force on Q 3 can never be zero, no matter what the (non-zero!) charge Q 3 is. 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 Q 3. D) The answer to above depends on the magnitudes of Q 1 and Q 2.

Lecture 1-19 Physics 241 – 10:30 Quiz 3 – Jan. 12, 2010 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.) e = 1.6  C k = 8.99  10 9 Nm 2 /C 2 A)to the right of charge –Q B) to the left of charge 2Q C) between the two charges D) some other place E) nowhere 2Q - Q d

Lecture 1-20 Physics 241 – 11:30 Quiz 3 – Jan. 12, 2010 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.) e = 1.6  C k = 8.99  10 9 Nm 2 /C 2 A)to the right of charge -2Q B) to the left of charge Q C)  between the two charges D) some other place E) nowhere Q - 2 Q d

Lecture 1-21 Physics 241 – Sample Quiz C – Jan. 8, 2008 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.) e = 1.6  C k = 8.99  10 9 Nm 2 /C 2 a) to the right of charge Q b) to the left of charge 2Q c)  between the two charges d) some other place e) nowhere 2Q Q d