Physics 1B Electricity & Magne4sm

Transcription

1 Physics 1B Electricity & Magne4sm Frank Wuerthwein (Prof) Edward Ronan (TA) UCSD

2 Outline of Today Administra4ve details of how this course works. Introductory overview of the quarter s material.

3 Introduc4on Welcome to Physics 1B! Physics 1 is a three quarter course designed as an introduction into basic physics for students in the biological sciences. Physics 1B in particular will focus on electricity and magnetism. Please note that the lecture and the lab are separate courses with separate instructors.

4 Lecture Hall and my office My office = MHA 5515 Lecture Hall = York 2722

5 Web site Contains all info about this course Course schedule Suggested Homework Syllabus Announcements Lecture notes (typically by noon of the day of the lecture).. and more. hvp://hepuser.ucsd.edu/twiki2/bin/view/ucsdtier2/physics1bwinter2012

6 Textbook Serway & JeweV, Principle of Physics 1, Vol. II Chapters The suggested homework are all from this book. Some solu4ons are in the back of the book. The rest will be on the web site before the quiz

7 Problem Solving Sessions Thursday 7-8:50pm 1 st Session on January 12 th!!! Center Hall 119 The TA will go over the suggested homework. The quiz ques4ons will tend to be similar to the suggested homework. While the homework is op4onal, doing it is worth your while.

8 Grading There are 4 Quizzes that make up 60% of the total grade: Friday January 27 th Monday February 13 th Friday February 24 th Monday March 12 th All 4 quizzes count. There will be a make- up quiz during finals week for excused absences only. The remaining 40% is based on the final exam. Friday March 23 rd 3-5:59pm, loca4on TBA

9 Absolute Grading Scale Greater than 95 A A A B B B C C C- Greater then 40 D My personal expecta4on is an average score of around If it s any worse than that then I will assume I screwed up and adjust the scale in your favor. If it s bever than that, I ll congratulate you on a job well done. Less the 40 F

10 Course Overview Chapter 19: Electric Forces & Fields & Flux Chapter 20: Electric Poten4al, Capacitance, and Energy in the Electric Field Chapter 21: Electric Current, Resistance, Energy & Power, Circuits Chapter 22: Magne4c Fields and Forces Chapter 23: Inductance, AC, RL circuits, energy in the magne4c field Chapter 24: EM waves and Maxwell s equa4ons

11 Any more ques4ons? If not, then let s get started!

12 Electrical Charge Two types of electric charge exist in nature: Posi4ve charge Nega4ve charge Like charges repel one another Opposite charges avract one another Charges are addi4ve Charges can onen move around We call this conductance Bring two objects of the same amount of charge but opposite polarity together and they neutralize each other. An object with no net charge may simply have perfect balance between pos and neg amounts of charge.

13 Quan4zed Nature of Electrical Charge In the early 1900 s, R. Millikan performed an experiment that showed that all charge is a mul4ple of one fundamental unit of charge. This fundamental unit is the charge of the electron, symbolized as e. We refer to the charge of the electron as nega4ve. This is an arbitrary conven4on.

14 SI Unit of electric charge = Coulomb e!=!1.602x10 19!Coulombs. Electrons have a charge of e. Protons have a charge of +e. Neutrons have no charge.

15 Charge Conserva4on No maver how charge moves, it is always conserved. The net charge of the universe does not change. Charge is conserved in any closed system. We can not create or destroy net charge, we can only move charge from one place to another.

16 Simplified model of materials Materials are made up of (many) atoms. An atom has protons and neutrons as core, and electrons buzzing around it. Atoms bind into materials by sharing electrons via chemical bonds. In some materials, some of the electrons can move around freely over long distances. We call those materials conductors. Materials become charged because electrons are added or subtracted, i.e. nega4ve charges are transferred between them.

17 Induc4on In addition to adding or removing electrons, you can rearrange the electrons present in the object. For example, when you place a positively charged object next to a neutral object, the protons will be repulsed and the electrons will be attracted. This will lead to an overall attraction for the neutral object to the positively charged object.

18 Conductors Conductors Conductors are objects in which charges (electrons) can move freely through. Examples of conductors are aluminum, tungsten, platinum, and most other metals. If you put a charge on a small region of a conductor, the charge will distribute itself over the entire surface of the material.

19 Grounding a Conductor Once you have charged a conductor, how do discharge it (when you are done with your experiment)? You use the fact that the Earth is a big reservoir for electrons (it can accept or give as many electrons as you want). You need to make a pathway from the conductor to the Earth for the electrons to freely move. This is called grounding.

20 Insulators Insulators are objects in which charges (electrons) can NOT move freely. Examples of insulators are glass, plas4c, rubber, and wood. Put charge on a small region of an insulator, and that charge will remain in that region rather than spreading across the object.

21 For Next Time (FNT) Read chapter 19 Start working on the homework for chapter 19.