Lect01 - We eto Physics 212 lcom

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Unformatted text preview: We eto Physics 212 lcom http://online.physics.uiuc.edu/courses/phys212 This le ctureis VERY full. Ple sit ne to som onenice (The ase xt e . re won’t bee pty se m ats). Fe stival se ating up front 01 Physics 212 Le cture1, S 1 lide Physics 212 Le cture1 Today's C pts: once a) C oulom Law b’s b) S rposition upe 60 50 40 30 Unde rstand som e 20 10 0 Unde rstand all Unde rstand m ost Physics 212 Le cture1, S 2 lide 03 Physics 212 - I ntro http://online.physics.uiuc.edu/courses/phys212 Eve rything can befound online– GO THERE • • • • • You havewe base pre cture and pre b d -le s -flights duebe e ry le fore ve cture . be You havewe base hom work duee ry we k. b d e ve e Besureto com tepre cture2 and pre ple le flight 2 be 6 amon Thursday. fore Bring pe & note n book to le cture– you will beworking on proble s m Re r your clicke AS so you can se your participation grade giste r AP e . Labs & Discussions • • Discussion S ctions m e this we k e et e Labs start August 31st, m havepre donebe ! ust lab fore 05 Physics 212 Le cture1, S 3 lide How your gradewill becalculate d Prelectures: 50 Prelectures: Preflight's: 25 Preflight's: Lecture participation: 25 Lecture participation The lowest score is dropped and your top 22 HW/Quiz scores determine your grade out of 250. out Prelectures + Preflights + Lectures 13 Homework + 10 Quizzes Labs Hour exams (3 x 100 each) Final Exam 100 250 150 300 200 Bonus Points: You can earn up to 1 extra bonus point in every extra lecture (for a maximum of 25 bonus points for the semester) by getting the right answers to all of the clicker questions. getting At the end of the semester your lecture bonus points are At added to your HW/Quiz score (250 max). You can make up for several bad quizzes by answering correctly in class. 06 06 Physics 212 Le cture1, S 4 lide Q: What arethebe fits of participating ? ne A: You le m arn ore 30 Viewer 25 Non-Viewer Data from last year’s first exam 20 15 10 5 0 43 48 52 57 61 65 70 74 78 83 87 91 96 100 Exam Score S nts who… tude Vie d pre cture we -le s Ble through pre cture w -le s 07 Exam1 ave rage 80% 73% Physics 212 Le cture1, S 5 lide Clicke rs se arn ore n • Re arch shows you le m whe you talk! ach cture • 1 point for e le um • Maxim of 25 points! cture s – No EX’s BUT have28 le um cture • Maxim 1 bonus point/le I MPORTANT: Theclass ne door also is using i>clicke xt rs Wene d to run at a diffe nt fre ncy e re que 1. Powe On r 2. Hold ON/OFF until POWER light flashe s 09 3. Pre BB ss Physics 212 Le cture1, S 6 lide Music Who is the Artist? A) B) C) D) E) Ray Charles Solomon Burke Henry Butler Johnny Adams Otis Redding “Rediscovered” Soul singer from 60’s Absolutely Beautiful Voice BB Highly Recommended DVD: “One Night History of the Blues” Physics 212 Le cture1, S 7 lide C oulom Law: b’s Theforceon a chargedueto anothe chargeis proportional to theproduct of the r The charge and inve ly proportional to these s rse paration square d. q2 q1 r q1q2 F∝ 2 r Note S ve of you aske about r-hat .. Moreon that in a coupleof slide : e ral d s Theforceis always paralle to a lineconne l cting thecharge but thedire s, ction The de nds on thesigns of thecharge pe s: de q2 q2 q2 11 q1 q1 q1 Opposite signs attract Likes signs repel Physics 212 Le cture1, S 8 lide BB Balloons Taketwo balloons and rub the m Take both with a pie of cloth. Afte ce r you rub the the will: my you A) Attract e r Attract ach-othe B) Re l e pe r Re ach-othe C)Eithe – it de nds on them rial of thecloth r pe ate Eithe 13 Physics 212 Le cture1, S 9 lide Balloons I f thesam t hing is doneto both balloons the will e y sam acquirethesam sign charge e . sam The will re l ! y pe The + ++ + + ++ + 14 Physics 212 Le cture1, S 10 lide 10 Coulom Law b’s Our notation Our r F1,2 is theforceby 1 on 2 (think “by-on ”) by on by-on r r12 is thevector that points from1 to 2. f rom t o ˆ r12is theunit vector in thedirection of unit r kq1q2 ˆ F1,2 = 2 r1,2 r1,2 r r12 Exam s ple Exam I f thecharge havethesam sign, theforceby charge1 s e would bein thedire ction of r12 (to theright) r q1 on charge2 r r1,2 q2 F1,2 I f thecharge haveoppositesign, theforceby charge1 s would beoppositethedire ction of r12 (le ft) on charge2 r q1 F1,2 17 r r1,2 q2 Physics 212 Le cture1, S 11 lide 11 BB Exam : Coulom Force ple b Two pape rclips arese parate by 10 m te The you re ove1 e ctron frome atomon the d e rs. n m le ach f irst pape rclip and placeit on these cond one . • r q1q2 F = k 2 r12 ˆ r12 k= 9 x 109 N m2 / C2 electron charge = 1.6 x 10-19 Coulombs NA = 6.02 x 1023 What will thedire ction of theforcebe ? What A) Attractive B) Re pulsive 17 Physics 212 Le cture1, S 12 lide 12 BB Exam : Coulom Force ple b Two pape rclips arese parate by 10 m te The you re ove1 e ctron frome atomon the d e rs. n m le ach f irst pape rclip and placeit on these cond one . • r q1q2 F = k 2 r12 ˆ r12 k= 9 x 109 N m2 / C2 electron charge = 1.6 x 10-19 Coulombs NA = 6.02 x 1023 Which we is close to theapproxim forcebe e those ight st ate twe n pape rclips (re that we = m g = 9.8 m 2)? call ight g, /s A) Pape rclip (1g x g) Pape B) Te book (1kg x g) xt C)Truck (104 kg x g) Truck D) Aircraft carrie (108 kg x g) r (10 E) Mt. Eve st (1014 kg x g) re Mt. 22 Physics 212 Le cture1, S 13 lide 13 BB Preflight 1 Preflight 70 60 50 40 30 20 10 0 “S inceQ is m large in m uch r agnitude it will havea m large , uch r forceon q than q will haveon Q. ” f orce “Theforceon e m bee ach ust qual and oppositeto satisfy Ne wton's The third law .” t hird A 24 BC Physics 212 Le cture1, S 14 lide 14 S rposition: upe I f the arem than two charge pre nt, thetotal forceon any give chargeis re ore s se n just theve sumof theforce dueto e of theothe charge ctor s ach r s: ve q2 F2,1 F4,1 F 1 F3,1 q1 F 1 F2,1 F4,1 F3,1 q4 q3 r r rr F1 = F2,1 + F3,1 + F4,1 + ... 28 Physics 212 Le cture1, S 15 lide 15 BB S rposition AC upe T What happe to Forceon q1 if its sign is change ns d A) | F1| incre s ase B) | F1| re ains thesam m e C) | F1| de ase cre s D) Ne d m inform e ore ation to de rm te ine q2 q1 q4 q3 30 Physics 212 Le cture1, S 16 lide 16 Thedire ction of all force change by 180o – t hem s s agnitude stay thesam : s e Thedire q2 F4,1 F4,1 q2 q1 F 1 F2,1 F q1 F3,1 F2,1 F3,1 q4 F F2,1 1 1 q4 F F2,1 1 q3 q3 F3,1 F4,1 F3,1 F4,1 r r rr F1 = F2,1 + F3,1 + F4,1 + ... 33 r r r r − F1 = − F2,1 − F3,1 − F4,1 − ... Physics 212 Le cture1, S 17 lide 17 Try using our Coulomb Force simulation Physics 212 Le cture1, S 18 lide 18 BB Pre flight +Q +Q Compare the magnitude of the net force on q in the two cases. A) B) C) D) 70 60 50 40 30 20 10 0 |F1 | > |F2| |F1 | = |F2| |F1 |< |F2| Depends on sign of q q F -Q 1 q F =0 +Q 2 Case 1 Case 2 A B CD There would be no net charge on Case 1, the charges applied on q by +Q and -Q are equal and opposite in direction, canceling out any net charge. In Case 2, though, +Q and +Q both apply a charge in the same (positive) direction, causing a positive net charge on q. The forces cancel out in case 2, while they add in case 1 It depends on the charge of q to know whether or not it will attract or repel. 33 Physics 212 Le cture1, S 19 lide 19 Pre flight Four charge particle areplace on a circular ring d s d with radius 3 mas shown be low. A particlewith chargeQ is place in thece r of thering d nte y What is thedire ction of horizontal forceon What Q? Q? A) Fx > 0 B) Fx = 0 100 80 60 40 20 0 3q x C Fx < 0 ) Q q q q Gre Job ! at 41 Physics 212 Le cture1, S 20 lide 20 Pre flight Four charge particle areplace on a circular ring d s d with radius 3 mas shown be low. A particlewith chargeQ is place in thece r of thering d nte BB 3q Q y x What is ve rtical forceon Q? A) Fy > 0 B) Fy = 0 60 50 40 30 20 10 0 C Fy < 0 ) q q q A B C The y component would be positive due to the fact that two of the three seperated q charges have an x component and a smaller y component than the 3q charge which is solely in the y direction. The distance of all four charges from charge Q are the same and magnitude from the 3 q charges would be equivalent to the 3q charge. Two of the lower q's have x compenents in their force vectors on Q so the force from 3q will be stronger than the bottom 3 q's in its y component 47 Physics 212 Le cture1, S 21 lide 21 3q Q q q q Try using our Coulomb Force simulation Physics 212 Le cture1, S 22 lide 22 Pre flight Four charge particle areplace on a circular ring d s d with radius 3 mas shown be low. A particlewith chargeQ is place in thece r of thering d nte BB 3q Q y x What is ve rtical forceon Q? A) Fy > 0 B) Fy = 0 60 50 40 30 20 10 0 C Fy < 0 ) q q q A B C The y component would be positive due to the fact that two of the three seperated q charges have an x component and a smaller y component than the 3q charge which is solely in the y direction. The distance of all four charges from charge Q are the same and magnitude from the 3 q charges would be equivalent to the 3q charge. Two of the lower q's have x compenents in their force vectors on Q so the force from 3q will be stronger than the bottom 3 q's in its y component 47 Physics 212 Le cture1, S 23 lide 23 That’s All Folks! e et e • Discussion S ctions m e this we k! ple le flight 2 be 6am fore • Besureto com tepre cture2 and pre Thursday gin • Labs be August 31st. Physics 212 Le cture1, S 24 lide 24 ...
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