Electricity and Magnetism Overview of Course Charge and Conduction

Transcription

1 Electricity and Magnetism Overview of Course Charge and Conduction Lana Sheridan De Anza College Sept 22, 2015

2 Overview of the Course Topics charge static electric interactions electric fields electric potential capacitance current, resistance, circuits magnetic fields, induction alternating currents Maxwell s equations

3 Overview of the Course Should I take this course? You should if: You enjoy physics and other technical subjects. You are curious about how nature works. You will spend time on your own thinking through concepts and problems.

4 Overview of the Course Should I take this course? You should if: You enjoy physics and other technical subjects. You are curious about how nature works. You will spend time on your own thinking through concepts and problems. You not should if: You just want an easy A. You just want to memorize answers without understanding them. You will not make time to work on problems outside of class.

5 Overview of the Course Book Fundamentals of Physics Extended, 9th Edition, Halliday, Resnick, and Walker We will cover chapters of this textbook. Other Books Physics: Principles with Applications, Giancoli (no calculus) Physics: A Strategic Approach, Knight (calculus with clear explanation)

6 Useful Survival Trick

7 Useful Survival Trick

8 Useful Survival Trick When you get stuck, use a search engine.

9 Other Resources Resources for when you have questions Me. You can me, ask me before or after class, or come to my office hour. Each other. Work together! It will improve your understanding. The Math & Science Tutorial Center. Where to look for course materials Course Studio. My website on the De Anza Physics page.

10 Overview of the Course Evaluation Midterm and Final exam. Weekly quizzes. Labs. Assignments Uncollected homework problems from the textbook. (You still need to do them.) A few collected homework worksheets. Read the textbook.

11 Overview of the Course Evaluation quizzes & worksheets 30% midterm 20% final 30% labs 20% Projected Grading Scheme: 88% 100% = A 76% 87% = B 65% 75% = C 54% 64% = D 0% 53% = F

12 Overview of the Course Note about presentation of work For each problem make sure your method is clear. If there is an equation or principle you are using, write it out at the start of your solution. Underline, box, highlight, or unambiguously emphasize the answer. If the reasoning is not clear, the answer is not correct. Give your answers to a reasonable number of significant figures.

13 Overview of the Course Note about collected assignments If you cannot come to class on a due date, me the assignment and bring the hard copy to the next class. If you are ill, or will have a problem handing in an assignment on time, come talk to me before the due date.

14 Electricity and Magnetism Imagine yourself in the world of 1700.

15 Electricity and Magnetism Imagine yourself in the world of no fast, long distance communication

16 Electricity and Magnetism Imagine yourself in the world of no fast, long distance communication it was almost impossible to work after sunset

17 Electricity and Magnetism Imagine yourself in the world of no fast, long distance communication it was almost impossible to work after sunset indoor heating meant burning something

18 Electricity and Magnetism Imagine yourself in the world of no fast, long distance communication it was almost impossible to work after sunset indoor heating meant burning something almost no mass-manufacturing

19 Electricity and Magnetism Imagine yourself in the world of no fast, long distance communication it was almost impossible to work after sunset indoor heating meant burning something almost no mass-manufacturing no household appliances

20 Electricity and Magnetism Imagine yourself in the world of no fast, long distance communication it was almost impossible to work after sunset indoor heating meant burning something almost no mass-manufacturing no household appliances no stereos, electric guitars, televisions, phones

21 Electricity and Magnetism Imagine yourself in the world of no fast, long distance communication it was almost impossible to work after sunset indoor heating meant burning something almost no mass-manufacturing no household appliances no stereos, electric guitars, televisions, phones What changed?

22 Electricity and Magnetism Electricity isn t new: Ancient philosophers, including Greek philosophers, were aware of both electric and magnetic phenomena. It was not until 1820 that Hans Christian Ørsted realized by accident that electricity and magnetism were related.

23 Electricity and Magnetism Goals: know how to use EM theory to solve problems understanding EM principles and how they apply to technology have a feeling for the scope of EM theory

24 Quick Reminder: What is Physics? Physics is the science of fundamental interactions of matter and energy.

25 Quick Reminder: What is Physics? Physics is the science of fundamental interactions of matter and energy. How is it done? Make a simplified model of the system of interest, then apply a principle to make a quantitative prediction.

26 Quick Reminder: What is Physics? Physics is the science of fundamental interactions of matter and energy. How is it done? Make a simplified model of the system of interest, then apply a principle to make a quantitative prediction. System Any physical object or group of objects about which we would like to make quantitative predictions.

27 Quick Reminder: What is Physics? Physics is the science of fundamental interactions of matter and energy. How is it done? Make a simplified model of the system of interest, then apply a principle to make a quantitative prediction. System Any physical object or group of objects about which we would like to make quantitative predictions. Model A simplified description of a system and its interactions that includes only what is necessary to make predictions.

28 Overview electric charge conductors insulators induced charge Force from a point charge Force from many charges

29 Electric Charge Charge is an intrinsic property of subatomic particles. Charge can be positive or negative. Particles can also be chargeless, ie. have zero net charge.

30 Electric Charge Charge is an intrinsic property of subatomic particles. Charge can be positive or negative. Particles can also be chargeless, ie. have zero net charge. The unit for charge is the Coulomb, written with the symbol C.

31 Charges of some particles Atoms are composed of electrons and a nucleus. Electrons are negatively charged. Nuclei have a positive charge: protons have positive charge neutrons are neutrally charged 1 Figure from Wikipedia.

32 Electric Charge on larger objects Before there was any knowledge of atoms, charge was imagined as a kind of continuous fluid. A large scale effect: In dry weather, it is easy to get a shock from static electricity. This is due to a charge imbalance.

33 Charge on larger objects Glass Most large objects around us have (approximately) zero net charge. + Glass Objects can become charged when rubbed against one another. F (a) These examples reveal carpets, doorknobs, faucets, amount of electric charge. fundamental particles makin automatically with those par F The vast amount of cha Glass the object contains equal am Glass negative charge. With such a Glass F F to be electrically neutral; th Plastic F charge are not in balance, (a) charged to (b) indicate that it ha 1 Diagrams from Halliday, Resnick, Fig. Walker, 21-29thalways (a) ed. Two much charged smaller rods of the than 2 CHAPTER 21 ELECTRIC CHARGE F

34 Electrostatic force Charged objects exert a force on one another. Charges with the same electrical sign repel each other. Charges with opposite electrical signs attract each other.

35 Electrostatic force Charged objects exert a force on one another. Charges with the same electrical sign repel each other. Charges with opposite electrical signs attract each other. Charged objects can also attract neutral objects by charge induction or polarization.

36 Some Vocabulary electrically neutral An object is electrically neutral if its net charge is zero. electrically isolated An object is electrically isolated if it cannot exchange charge with its surroundings.

37 Conductors and Insulators Some materials allow charges to flow through them easily, some do not.

38 Conductors and Insulators Some materials allow charges to flow through them easily, some do not. Conductors materials through which charge can move readily Insulators (also called nonconductors) are materials that charge cannot move through freely

39 onduction Induced Charge electrons. There are few (if any) If a conductor is brought close to a charged object, positive and negative charges in the conductor start to separate and we say a charge is induced on the conductor. nstrates the mobility of charge in a conducwill attract either end of an isolated neutral rically isonded on a opper rod onduction the far end lastic rod. aining posirod, rotating er to the Neutral copper F F Charged plastic

40 realignment of charges in Induced Chargethe Polarization molecules of the wall. in th Charged balloon a Wall Induced charge separation b

41 Course Tool Quiz Socket Allows me to ask multiple choice questions or do surveys, and get real-time feedback. You remain anonymous. You need a device connected to the internet. Load the webpage ( and enter the quiz id.

42 he molecules to emit ultraviolet light. You cannot see this type of er, Question the wintergreen molecules on the surfaces of the candy pieces ltraviolet light and then emit blue light, which you can see it is the ing from your friend s mouth. A, B, and D are charged pieces of plastic. C is an electrically neutral copper plate. OINT 1 shows five s: A, B, and ged plastic A C C D B is an electral copper electrostatic en the pairs shown for B A D A D pairs. For the remaining two pairs, do the plates repel or attract each other? Plates C and D (A) attract each other (B) repel each other 1 Page 564, Halliday, Resnick, Walker, 9th ed.

43 he molecules to emit ultraviolet light. You cannot see this type of er, Question the wintergreen molecules on the surfaces of the candy pieces ltraviolet light and then emit blue light, which you can see it is the ing from your friend s mouth. A, B, and D are charged pieces of plastic. C is an electrically neutral copper plate. OINT 1 shows five s: A, B, and ged plastic A C C D B is an electral copper electrostatic en the pairs shown for B A D A D pairs. For the remaining two pairs, do the plates repel or attract each other? Plates C and D (A) attract each other (B) repel each other 1 Page 564, Halliday, Resnick, Walker, 9th ed.

44 he molecules to emit ultraviolet light. You cannot see this type of er, Question the wintergreen molecules on the surfaces of the candy pieces ltraviolet light and then emit blue light, which you can see it is the ing from your friend s mouth. A, B, and D are charged pieces of plastic. C is an electrically neutral copper plate. OINT 1 shows five s: A, B, and ged plastic A C C D B is an electral copper electrostatic en the pairs shown for B A D A D pairs. For the remaining two pairs, do the plates repel or attract each other? Plates B and D (A) attract each other (B) repel each other 1 Page 564, Halliday, Resnick, Walker, 9th ed.

45 he molecules to emit ultraviolet light. You cannot see this type of er, Question the wintergreen molecules on the surfaces of the candy pieces ltraviolet light and then emit blue light, which you can see it is the ing from your friend s mouth. A, B, and D are charged pieces of plastic. C is an electrically neutral copper plate. OINT 1 shows five s: A, B, and ged plastic A C C D B is an electral copper electrostatic en the pairs shown for B A D A D pairs. For the remaining two pairs, do the plates repel or attract each other? Plates B and D (A) attract each other (B) repel each other 1 Page 564, Halliday, Resnick, Walker, 9th ed.

46 equal numbers of positive Charging by Induction and negative charges. A conductor is initially neutrally charged. Electrons redistribute when a charged rod is brought close. 0 Figures from Serway & Jewett, 9th ed. a is li iden eno I occ 25.7 stan cre me has neu

47 Electrons redistribute when a Charging by Induction charged rod is brought close. A (negatively) charged object is brought close, polarizing the conductor. b Some electrons leave the grounded sphere through the ground wire. 0 Figures from Serway & Jewett, 9th ed. neu Q u W a A o o t

48 Some electrons leave the Charging by Induction grounded sphere through the ground wire. Excess (negative) charge on the far side is drawn off the conductor by grounding it. The excess positive charge is nonuniformly distributed. 0 Figures from Serway & Jewett, 9th ed. c 23. It is c throu Ele ele the bo Mater

49 The excess positive charge is Charging by Induction nonuniformly distributed. The conductor is isolated again. The remaining electrons redistribute uniformly, and there 0 Figures from Serway & Jewett, 9th ed. d b Mat insu bec the I con read S som man

50 is a net uniform distribution of Charging by Induction positive charge on the sphere. Figure 23.3 Charging a metallic object by induction. (a) A neutral The conductor is now (positively) charged. metallic sphere. (b) A charged rub- 0 Figures from Serway & Jewett, 9th ed. e cat hom ove ato T side in F if t is b rep

51 Summary content of the course charge conductors and insulators Force from a point charge Force from many charges Homework Get the textbook: Fundamentals of Physics Extended, 9th Edition, Halliday, Resnick, and Walker Read the Lab instructions for Thursday. Read Ch 21. Do the worksheet at getattachment/curriculum/estatics/static2.pdf