Lecture 1-1 Physics 241: Electricity and Optics Lecture 0201: 10:30 – 11:20 (T,Th) 0301: 11:30 – 12:20 (T,Th) Prof. Rolf Scharenberg Office: PHYS Room 245 Textbook: Physics for Scientists and Engineers (6 th edition ), volume 2 or newer by Paul A. Tipler and Gene Mosca Exams: 2 evening one-hour exams and a two-hour final exam Quizzes: during lectures using iClickers. Homework: CHIP (26 assignments) Course Web Page:: CHIP website: All Lectures take place in Rm. PHYS112 Lecture 0101: 9:30 – 10:20 (T,Th) Prof. Wei Xie Office: PHYS Room 246

Lecture 1-2 An Old (and Fundamental!) Question: What is the Structure of Matter in the Universe?

Lecture 1-3 Structure of matter in the Universe scale ~ m scale ~ m Huge scale Iron Wood Universe Gravitational Electromagnetic Strong Leptons: electron, muon, etc Current building block

Lecture 1-4 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 1-5 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 1-6 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 1-7 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 1-8 Warm-up Quiz 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? 1. The force on Q 3 can be zero only if Q 3 is placed to the left of Q The force on Q 3 can never be zero, no matter what the (non-zero!) charge Q 3 is. 2. The force on Q3 can be zero only if Q3 is placed between Q1 and Q2. 3. The answer to above depends on the sign of Q The answer to above depends on the magnitudes of Q 1 and Q 2.

Lecture 1-9 friction can cause electrons to move from one object to another.

Lecture 1-10 Charging by rubbing

Lecture 1-11 Charging by induction grounding polarization by induction

Lecture 1-12 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 1-13 Question A Human weight 120 lb, which of the following is correct? a)A large fraction of the weight come from the attraction force between the charges on human body and earth. b)All the weight comes the attraction force between the charges on human body and earth. c)All the weight come from the gravitational forces. The electric forces are negligible.

Lecture 1-14 Principle of Superposition q1q1 q2q2 q3q3 F 13 F 12 F1F1 Add by components or Magnitude and direction separately by using trigonometry

Lecture 1-15 Physics 241 – Sample Quiz A – 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

Lecture 1-16 Physics 241 – Sample Quiz B – 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 -2Q b) to the left of charge Q c)  between the two charges d) some other place e) nowhere Q - 2 Q d

Lecture 1-17 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