Exam 3, vers Physics Spring, 2003

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1 1 of 9 Exam 3, ves Physics Sping, 2003 NAME Signatue Student ID # TA s Name(Cicle one): Michael Scheffestein, Chis Kelle, Paisa Seelungsawat Stating time of you Tues ecitation (wite time in box: 9am, 1pm, etc) Please do not open the exam until you ae told to. You exam should have 10 pages, numbeed 1 thu 10. Thee is a blank sheet at the end fo scatch. This exam consists of 25 questions, woth 4 points each fo a total of 100 points. Fill in the bubble sheet with a #2 pencil. You must fill out you bubble sheet accoding to the following instuctions o you will automatically lose 10 points. Place a check in each box on the left as you complete the instuctions. Pint and bubble in you name and student ID on the bubble sheet. Pint and bubble in you Exam vesion, 0001 o 0002, in the uppe left of you bubble sheet in the aea maked Please leave the aeas labeled Code and Date blank Ease mistakes as thooughly as possible. Ask fo a fesh bubble sheet if you fea you cannot thooughly ease mistakes. As you take the exam, cicle the coect answes on you exam as well as making them on the bubble sheet. That way we can gade the exam, if you bubble sheet is lost. At the end of the exam, check that you have filled in the fist 25 questions on the bubble sheet, with only one bubble filled in fo each question. I have ead and followed the instuctions above. Signatue Possibly useful infomation: Coulomb's constant k = (SI units), e = C, µ 0 = 4π 10 7 (SI units) ε = (SI units)

2 2 of 9 1. A coil of wie with N = 2 loops is attached to a 1Ω esisto and is oiented pependicula to a unifom magnetic field as shown. At a paticula instant, the magnitude of the magnetic field is = 0.50 T and the field is DECREASING at a ate of 0.05 T/s. The aea of each loop is A = 0.50 m 2. What is the magnitude of the cuent though the esisto? A) 1.0 ma ) 20 ma C) 50 ma D) zeo E) None of these. R= 1Ω deceasing 2. In the poblem above, the diection of the cuent though the esisto is.. A) up ) down C) cuent is zeo 3. A hand-canked electical geneato is attached to a esisto R. The geneato is tuned at a constant ate which causes an AC cuent to flow in the esisto. Suddenly, the value of the esistance R deceases. Does the geneato get easie o hade to tun? A)Easie. ) Hade. C) No change in difficulty. 4. A step-down tansfome has N P =1000 tuns in the pimay coil and N S =100 tuns in the seconday coil. The pimay side is plugged into a standad 120V AC outlet, and the seconday side is attached to a R = 10 Ω esisto. To two-place pecision, what is the ms cuent dawn fom the outlet? A) 0.24 A ) 0.12 A C) 1.2 A D) 2.4 A E) None of these.

3 5. A solenoid has cicula coss-section and adius R. The cuent of the solenoid is steadily inceasing, ceating a unifom magnetic field within the solenoid which is inceasing at a steady ate, d/dt = constant.. What is the magnitude of the electic field E at a point outside the R solenoid a distance (>R) fom the cente of the solenoid? A)zeo D) 2π R d dt ) πr d 2 dt E) None of these. 2 C) R 2 d dt inceasing 3 of 9 6. An electon (q = e) is eleased fom est in a egion of space whee thee is constant, unifom, electic field E, and a constant, unifom magnetic field. The electic field points up and the magnetic field points into the page in the diagam. Which, if any, of the fou paths shown will the electon follow? (The fou paths ae in the plane of the pape.) E C) D) (in) A) ) E) None of these is coect. 7. A block of mass m, with a net positive chage q, is placed on a fictionless plane inclined at an angle θ. A unifom hoizontal extenal electic field of magnitude E is applied in the diection shown. How big does the electic field have to be so that the mass m stats to move up the incline? The E-field must be bigge than A) mg tan θ q ) qcos θ mg C) q mg sin θ D) mg cos θ q +q, m θ E) None of these E

4 4 of 9 8. A haidye with esistance R is plugged into a standad 120VAC wall socket (the ms voltage is 120V). The cuent though the haidye as a function of time is shown. Note that each tick mak along the y-axis is 2 A. What is the esistance R of the haidye (to two-place pecision)? A) 12 Ω ) 24 Ω C)17 Ω 10 I (A) 0-10 D) Ω E) 60 Ω time 9. A long staight wie, caying a cuent I, passes though the cente of a cicula wie loop. The wie loop is in the plane of the page, the staight wie is pependicula to the page, and cuent is going into the page and is deceasing. The cuent induced in the wie loop is A) counte-clockwise ) clockwise C) zeo I(in) deceasing wie loop 10. As indicated in the diagam, the magnetic field in a cetain egion is given by xy (, ) = Ayxˆ whee A is a positive constant. Conside the imaginay loop shown. What can you say about the cuent though the loop? A) The cuent though the loop must be zeo. ) Thee must be a non-zeo cuent though the loop coming out of the page. C) Thee must be a non-zeo cuent though the loop going into the page. D) You can say nothing about the cuent though the loop, on the basis on of the infomation given. y x

5 5 of The diagam shows the equipotential lines of a point chage located at the oigin. Note that the tic maks show 1 m spacing. What is the value of the chage? A) 1 µc ) 1 mc C) 10 6 C 10m 5m 2 kv 1 kv D) C E) None of these 3 kv 5m 10m 12. Two positive chages and a negative chage, all of equal magnitude (+Q, +Q, and Q) ae located at the thee cones of a squae of edge length. The oigin is the fouth cone of the squae. At the oigin, what is the diection of the electic field? y +Q Q A) ) E) None of these; eithe the field is zeo, o it points in some othe diection. +Q x C) D) 13. The same cuent I is flowing though solenoid A and solenoid, which both have cicula coss section. The solenoids have the same length, but solenoid A has twice the diamete and twice the numbe of tuns as solenoid. What is the atio of the magnetic enegy contained in solenoid A to UA that in solenoid, that is, what is U? (Hint: fo a solenoid = µ o n I ) A)2 )4 C)8 D)16 E) None of these. A

6 The next two questions efe to the following situation. A coaxial cable consists of an inne solid wie with adius R and an oute cylindical wie with inne adius 2R and oute adius 3R. The inne wie caies total cuent I into the page and the oute cylindical wie caies the same magnitude cuent I out of the page. oth wies have unifom cuent density. 14. What is the magnitude of the magnetic field at the inne suface of the inne wie, that is, at = 2R? A) zeo ) µ oi µ C) oi D) 3 µ oi 2πR 4 πr 2πR E) None of these. 6 of 9 R I(in) I(out) 2R 3R 15. What is the magnitude of the magnetic field at the suface of the oute wie, that is, at = 3R? A) zeo ) µ oi C) µ oi D) 3 µ oi E) None of these. 6πR 3πR 2πR 16. A single cicula loop of wie of adius R suounds a long solenoid of adius, tuns pe length n, caying a cuent I. Note that < R. The diagam shows the end-on view of the situation. What is the magnetic R flux though the single wie loop? A) µ o ni πr 2 ) µ o I 2 /(2R) C) πr 2 (µ o I/2π) D) µ o ni π 2 E) None of these. I solenoid

7 7 of A single-tun coil of wie with aea A = m 2 is otating in a unifom, constant extenal magnetic field. The magnetic flux Φ though the coil as a function of time is 5 shown in the figue. What is the maximum magnitude of the emf acoss the coil (to within 30%)? 0 A) 1 V ) zeo C) 4 V D) 0.3 V E) None of these. fluxφ(t m 2 ) time(s) 18. A loop of wie is falling staight down in a unifom magnetic, as shown. The magnetic foce on the loop is A) upwad ) downwad C) ight D) left E) zeo 19. Two cicula loops of wie lie in the same plane, as shown, with loop 2 just inside loop 1. A cuent in the oute loop (1) is counteclockwise (CCW), and is inceasing at a steady ate. The cuent induced in loop 2 is.. A)zeo ) clockwise (CW) C) counte-clockwise (CCW). 1 2 I inceasing

8 8 of 9 The next two questions efe to this situation. Thee paallel wies each cay a cuent of the same magnitude I. The 3 wies ae pependicula to the xy plane and fom a squae of edge length with the oigin, as shown in the diagam. Two of the cuents ae into the page, and one cuent is out of the page. 20. What is the diection of the magnetic field at the oigin? y I(in) I(out) A) ) E) None of these, eithe the -field is zeo at the oigin o has some othe diection. I(in) x C) D) 21. What is the magnitude of the -field at the cente of the squae (not at the oigin)? 3µ 0I 3µ 0I µ 0I µ 0I A) ) C) D) E) None of these. 2π 2π 2π 3π

9 9 of 9 The next two questions efe to the LR cicuit shown. The switch has been closed fo a long time. Then, at t = 0, the switch is opened. 22. What is the cuent though the inducto, immediately afte the switch is opened (at t = 0+)? A) zeo ) 1 A C) 2 A D) 0.5 A E) None of these 0.1 H switch 10 V 10 Ω 10 Ω 23. What is the voltage acoss the inducto immediately afte the switch is opened? A) zeo ) 10 V C) 5.0 V D) 2.5 V E) 30 V 24. Two long, staight, paallel vetical wies ae caying cuent. The ight wie caies a cuent upwad, as shown. Thee ae no othe cuents neaby. At a point which between the wies and nea the left wie the magnetic field is zeo. What is the diection of the cuent in the left wie? A) up ) down C) impossible to tell. = A wie caying a cuent I is in a unifom magnetic field (caused by an extenal magnet not shown in the diagam). The cuent I and the -field have the same diection, as shown. The foce on the wie due to the magnetic field is. A) ight ) left C) up D) down E) zeo I

ev dm e evd 2 m e 1 2 ev2 B) e 2 0 dm e D) m e

ev dm e evd 2 m e 1 2 ev2 B) e 2 0 dm e D) m e . A paallel-plate capacito has sepaation d. The potential diffeence between the plates is V. If an electon with chage e and mass m e is eleased fom est fom the negative plate, its speed when it eaches