PHYS 241 Electricity & Optics

Transcription

1 PHYS 241 Electricity & Optics Physics Department Home page: Course Home page: CHIP Home page: Piazza: Room 144 Undergraduate office Room 11 Help center Room 290 Physics Library

2 Course Home page:

3 Calendar *Read the assigned Chapter sections prior to attending class. *Note Exam Dates *Homework is due on Mondays at 11:59 PM. Homework is done through CHIP. CHIP Home page:

4 Syllabus Questions about grades, grade checks, absences, etc please see Prof. Pyrak Nolte

5 Syllabus *Register your I clicker on CHIP. *Always bring your I clicker to class. *5% of your point total is based on lecture quizzes. CHIP:

6 Syllabus

7 Online Forum We will use Piazza for class discussions to assist you in getting help fast and efficiently from your classmates and the teaching assistants. Rather than ing questions to the teaching staff, you are encouraged to post your questions on Piazza: You can sign up for a Piazza account and enroll in our class page at:

8 Additional Resource: Short YouTube Videos on selected topics.

9 CLICKER LOG IN (1point)

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

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

12 Concept of Charge Charging by rubbing

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

14 DEMO #5A01 STATIC ELECTRICITY

15 CHARGING BY INDUCTION polarization by induction grounding

16 DEMO # 5A 06 BRAUN, GOLD LEAF, 2 x4 ELECTROSCOPES

17 QUANTIZATION OF CHARGE Fundamental unit: elementary charge e q ne, n 1, 2, 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 1second when there is a current of 1 ampere in the wire e C C 3,

18 CONDUCTORS AND INSULATORS 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

19 CONSERVATION OF CHARGE The net electric charge is conserved in any physical process. But Charge can be transferred from one object to another. Zn() s 2 H ( aq) SO ( aq) Zn SO ( aq) H ( g) Individual charges can also, in fact, be destroyed or created, but not net charges e ( annihilation) e ( pair production)

20 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. r1,2 q 1 q 2 qq F k r 1,2 1 2ˆ 2 1,2 r1,2 Coulomb constant: k by 1 on N m 2 r / C where is called the permittivity constant. 2

21 How strong are Coulomb forces? Electron and proton in a hydrogen atom Compare electric and gravitational forces F F F electron and proton e e k r ke Gm m g p e ( Nm / C )( C) 11 2 a F/ me ( m) 7 (10 ) 30 O N O(10 ) kg 2 e mm p e Fe k F 2 g G 2 r r m e = 9.11x10 31 kg, 39 O O(10 ) m/ s 23 2 m p =1.67x10 27 kg 7 (10 ) N G = 6.67 x10 11 m 3 s 2 kg

22 Principle of Superposition F F12 F F q 1 F 13 q 3 q 2 F 12 F1 Graphical addition OR by Magnitude and direction separately by using trigonometry

23 Physics :30 Quiz (1point) January 13, 2014 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.) 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 d Q e= 1.6 x C k= 8.99 x 10 9 Nm 2 /C 2

24 Physics 241 Extra Quiz 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.) 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 d Q e= 1.6 x10 19 C k= 8.99 x 10 9 Nm 2 /C 2