PHYSICS 272 Electric & Magnetic Interactions. Prof. Andrew Hirsch Room: 178, Phone: 42218

Transcription

1 PHYSICS 7 Electic & Magnetic Inteactions Pof. Andew Hisch Hisch@pudue.edu Room: 78, Phone: 48

2 Couse Content This couse deals with electic and magnetic inteactions, which ae cental to the stuctue of matte, to chemical and biological phenomena, and to the design and opeation of most moden technology. The main goal of this couse is to have you engage in a pocess cental to science: the attempt to model a boad ange of physical phenomena using a small set of poweful fundamental pinciples. The specific focus of the couse is an intoduction to field theoy, in tems of the classical theoy of electicity and magnetism (E&M). The couse also emphasizes the atomic stuctue of matte, especially the ole of electons and potons in matte.

3 Schedule Lectues: Monday, Wednesday 0:30 - :0 Lectue Room: PHYS Instucto: Pof. Andew Hisch Office hous: by appointment Office: PHYS 78, Phone: (49)-48 hisch@pudue.edu (please use subject: PHYS 7) Teaching Assistants: David Blasing, John Doyle, Jonathan Nisto, Justin Sheek Couse infomation: Undegaduate Office - PHYS 44

4 Textbook The textbook is Matte & Inteactions, vol II: Electic & Magnetic Inteactions by R. Chabay & B. Shewood (John Wiley & Sons 007). We will cove almost all of the topics in this volume. See the table of contents at the font of the book (which also includes the contents of Volume I). Make sue it is the Thid Edition. The new book comes with a fee coupon fo WebAssign, the on-line homewok sevice. Follow the instuctions and get youself egisteed.

5 Geneal Infomation Room PHYS 44: Undegaduate office Room PHYS : Help cente Room PHYS 90: Physics Libay We will use WebAssign fo homewok and lab assignments. You will be able to access you scoes in CHIP. See Impotant Links on couse web page fo details Fo uestions concening WebAssign contact: V.K. Saxena: Office: PHYS 76, Phone: 49575

6 Activities and Responsibilities In-class activities and esponsibilities You ae esponsible fo attending all classes, and attendance will count towad you gade. Bing a scientific calculato to class. If you miss class, it is you esponsibility to find out what you missed. Lectues slides will be available shotly afte lectue concludes. Homewok Homewok and lab assignments will be posted on the web. See WebAssign (and Calenda section) fo due dates. Outside class Study assigned textbook sections. An assignment to study sections of the textbook means: Read the assigned textbook sections thoughtfully. Do the "stop and think" activities. Wite bief solutions to the in-line "execises" and keep them in a notebook.

7 Quizzes, Exams, Gades Clicke Questions in Lectue: Shot multiple choice uestions will be posed in lectue. The pupose is to assess you undestanding. It will also be used to check attendance. We will stat counting clicke uestions towads you gade at lectue #5. You have to puchase an iclicke ( ) fom the bookstoe. You must egiste you clicke ID in CHIP Exams: Thee will be two -hou exams and a -hou final exam. All exams ae closed-book, but elevant fomulas and constants will be povided. Gades: The final gade will be detemined on the following basis (Couse Total = 700 points): 00 points - final exam 00 points each - two -hou exams (Feb 8, Mach ) 75 points - WebAssign homewok 00 points Labs 5 points - Clicke Questions & Attendance 00 points Recitation Poblems

8 This Week Study chaptes 4 and 5. Lab will stat this Wed. Do not fall behind

9 Clicke Question A) Engineeing B) Science C) Libeal Ats D) Education E) Othe Set you clicke feuency to AB My majo is

10 Clicke Question A) Physics B) Physics C) Physics D) Physics Ε) Πηψσιχσ My favoite subject is

11 Electic and Magnetic Fields Electic and magnetic fields manifest thei existence though inteactions with matte Maxwell euations: " div( E) = $ # E = 0 div( B) = " B = 0 cul( E) = " E = # $B" $t & cul( B) = ) ( B = µ 0$ J + * % 0 ' E ' t # " Loentz foce: F = E + v B

12 Point Chages Two types: positive and negative Like chages: epel Opposite chages: attact Chage is uantized in units of e Millikan s oil dop expeiment (90-93) Point chage: Size is small compaed to the distance between it and othe objects of inteest Electic chage is an intinsic popety of the fundamental paticles that eveything is made of

13 F = The Coulomb Foce Law F = 4" 0 Q Q "The magnitude of the electostatic foce between two point chages is diectly popotional to the magnitudes of each chage and invesely popotional to the suae of the distance between the chages." Q Q Chales-Augustin de Coulomb ( ) F F

14 F = The Coulomb Foce Law 4" 0 Q Q ˆ ε 0 = pemittivity constant + + Foce epulsive F Foce on by + F - Foce attactive The foce exeted by one point chage on anothe acts along line joining the chages. The foce is epulsive if the chages have the same sign and attactive if the chages have opposite signs.

15 Units and Constants SI units of electic chage: Coulomb, C Constants: F = F /4πε 0 = 9x0 9 N. m /C ε 0 = 8.85x0 - C /N. m pemittivity constant e =.60x0-9 C " C = 6.4x0 8 elementay chages Paticle Chage electon -e positon +e poton +e antipoton -e muon +e o e pion +e o e o 0 neuton 0 = 4" 0 Q Q

16 Matte consists of atoms cm 3 : ~0 4 atoms Stuctue of Atom Nucleus: ~0 4 times smalle than electon cloud, ~0 4 times heavie than electon. Å=0-0 m Example: nucleus of the ion atom Size: ~0 5 m, mass: ~0-5 kg Nucleus chage = +Ze, atom with Z electons is neutal.

17 The Concept of Electic Field Acceleates at 9.8 m/s why? Acceleates at 0 m/s why? Thee ae many possible configuations of chages to poduce the obseved effect.

18 Electic Field Thee is something in space waiting fo a chaged paticle to inteact with it This vitual foce is called electic field. An electic field ceated by chage is pesent thoughout space at all times, whethe o not thee is anothe chage aound to feel its effect.

19 Definition of Electic Field E F = " # $ $ % & = = F F '( '( / F E =

20 Electic Field E = F / If ou pobe chage is positive o negative F due to given E will point in coect diection. E E,,, ( x y z t) Electic field has units of Newtons pe Coulomb: [N/C]

21 " # $ $ % & = 0 4 F '( E F = 0 4 E " = E ˆ 4 0 " = Including diection: 3_E_point_chage_dag.py The Electic Field of a Point Chage + -

22 Example Poblem A paticle with chage + nc ( nanocoulomb=0-9 C) is located at the oigin. What is the electic field due to this paticle at a location <-0.,-0.,-0.> m? Solution:. Distance and diection: = obseved _ location souce_ location = 0.,0.,0. 0, 0, 0 = 0.,0.,0. = 0. ˆ = ( ) + (0.) + (0.) = 0.35 m = 0.,0., E = 0.57,0.57,0.57 = 4" 0 ˆ

23 Example Poblem. The magnitude of the electic field: E Nm C 9 #& ' 0 C "% 0.35 m ( & = 9 $ 9 0 $ = ' 4)* 0 % # " E = 47 N C = 4" 0 ˆ 3. The electic field in vecto fom: E E = = Eˆ ' N $ = % 47 " & C # 84, 84, , 0.57, 0.57 N C

24 The Physical Concept of Field Field: physical uantity, can be scala o vecto Examples: Tempeatue T(x,y,z,t) Ai flow, gavitational field m F = F = mg E

25 Foces due to an Electic Field Example: The electic field at a paticula location is <-300,0,0> N/C. What foce would an electon expeience if it wee placed in this location? Y E e F X Solution: F = ee =.6 " 0 9 C 300,0,0 N/C F = 4.8" 0 7,0,0 N