Phys 1120 exam1_soln - i PHYSICS 1120 FIRSTMIDTERM Name...

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Unformatted text preview: i PHYSICS 1120 FIRSTMIDTERM Name gfll U CS\/\ Student ID # Section number and TA Name: Exam Version 0001 Please do not open the exam until you are asked to. ° Your exam should have 10 pages, numbered El .1 thru 131.10 This exam consists of 15 multiple choice questions, worth 5 points each, and a long—answer section worth 25 points, for a total of 100 points. Write your answers in the space provided on each page for the written question. Use the back of the page if needed. Circle the correct letter for the multiple choice questions. SHOW YOUR WORK ON THE WRITTEN QUESTIONS. Full credit will be given only for the correct answer accompanied by your reasoning. PLEASEX! 1. Print your name on each page in the space provided. - 2. Print your student Identification Number on the page above. 3. Bubble your name, ID, and exam version number on the bubble sheet provided in the 1234 columns. 4. Write the name of your TA neatly in the big blank space at the bottom of the bubble sheet. Our TA's names are Matt Aitken, Maya F abrikant, Nathan Hinkley, Sum'ta Kannan, Nathan Morrison, John Papaioannou, Ron Pepino By handing in this exam, you agree to the following statement: "On my honor, as a University of Colorado Student, I have neither given nor received unauthorized assistance on this work" Signature Possibly useful information: k = 9.0X109 NmZ/CZ, basic charge unit 1.6x10‘19 C, so = 8.85x10‘12 CZ/(Nm2) G : 6.7xl0‘“ N.m2/kg2 Good luck! Spring 2010 El .1 V1 First Midterm Circle the closest answer and Bubble in questions 1-15 ON YOUR BUBBLE SHEET! 1. A glass rod has an initial charge of +6 mC. The rod is rubbed with a neutral cloth. After the rubbing, the rod has a final charge of +3 mC ’fine, (Q9! ‘ 0Q“ A) Conservation of charge requires that the cloth now has a +6 mC net charge. 3? m C, Conservation of charge requires that the cloth now has a +3 mC net charge. 5 l J “NFC ) Conservation of charge requires that the cloth now his a —3 mC net charge. C , " > D) Conservation of charge requires that electrons move to the cloth. ‘3’»?de ~93 M C; E) Conservation of charge requires that both objects remain neutral. 2. A negatively charged rod is brought close to an conducting sphere as shown below. There is no net charge on the conductor. Some time later the negatively charged rod is removed and a positively charged rod is moved close to the sphere. What effect if any do the rods have on the sphere? Assume that the rods never come in contact with the sphere. uncharged uncharged conducting conducting sphere sphere negatively positively charged rod charged rod . _\_ m ‘phere is attracted to both of the rods C Man/fies “A“ Move B) Sphere is repelled by both rods AMA C’l’l W C (At! V646 g Wlll be ( (05.9 V‘ C) Sphere has no net charge and is not affected by either rod + ' D) Sphere is attracted to the - charged rod, and repelled by the + charged one 0 m Vfl/ E) Sphere is repelled by the — Charged rod, and attracted to the + charged one i” MY? WM be a. wet qfimwmn 3. A charge of Q0 Coulombs sits at the origin. A test charge of Qp sits at point P, as shown below. The two charges are separated by a distance d. What is the magnitude of the electric field the test charge Qp experiences ? d W»:- A) on/d WO/d2 ‘ C) onQp/d2 D) ka/d E) l’ch/d2 Spring 2010 El .2 V1 First Midterm The following two questions refer to this situation: Two particles, both with negative charge -2 C, are located on the x—axis as shown below. A particle with charge +1 C is placed on the y-axis. +1 C (0m, 4m) —2C 4. What is the direction of the net force on the positively charged particle placed at point P? A) —> 2) <- . /\ Hot/QC Vii’otl mmwmifi @fi Cat/ice! t ‘ Verhml E) There is no net force aafir 0W3 WM ‘ 5. What is the magnitude of the force on the particle at point P? .— 3m 1': géiéfi mW95W\ B—’*leqmt 3590 Q 1.1592”; 9 ' kQ\QE ‘ 33 gay; 3.; Wm «6 ENC, :. N 6. Which graph mos‘tycloselyZQF‘5 ‘ ' l 5 X ’00, M Qow‘ ba’fifl C m y {ii/(Si represents the X—component of _ Charged C5 the electric field along the x—axis ring for a uniformly negatively +X‘aXIS charged ring centered at the —~—-—>) 6‘... origin (0,0) as shown to the - right? A) Ex B) Ex Alijr {pm‘x’t‘afif’i} imWw Y (O X 5C: Klein/"323 “3’49 "WM: 1&%[email protected]?%M3amw xf> 0 ' ~ Ea. O “A, V190 Spring 2010 First Midterm 7. The figure below shows the electric field for two point charges. Which of the following statements about this figure are true? XI. Q1 and Q2 have the same sign II A negative charge placed at point C will move right ‘ — Una { S ><III The magnitude of the electric field at point a is greater than at page. VVl 0N 0‘- V Der/15113 0f; 1-1111?“ 11mg; (16% was, awouj A) None are true - B) I II and III are true ”‘6de g AQYOM C97, C) II & III are true Jq“ i’ 0’1 ”iii/1311:1394 it” . 8. A proton (q=+l 6111019 C, m=l .67xlO'27 kg) is released from rest in a uniform electric field of ‘ 0.001 N/C. What is its speed 2 seconds after it is released? A) Um/s YZCE(6 :: m 0K, Bamaauqurvs 11 1 g .11 001 ‘9 / I 1 01 Q as ‘ a1 « 5Q ~- “seesaw ”mm W 24 M 1.921110”; ,7 D) 1.2x10 m/s a 1 4‘5 Boo WI/ 2 E) 3.2x10‘22 m/s 1 ‘ l S! 1/15 +1911” 2 01 (27;,me 1 ,11 N700 m/S 9. An object with a charge +2C and mass 0.5 ngDs placed 1n a uniform electric field of strength +5 N/ C. What 15 the magnitude of the force on the object? A) UN B)2.5N C)5N D)7N @ F: E?) 1: Sky/C 1, 06C ‘2 {0N Spring 2010 E14 Vl First Midterm The next two problems refer to the following figure. A closed cube is placed in a uniform electric field E:( 2i, 3)“, 416) N/C. Each side of the cube is 1m in length. There are no charges inside the cube. 10. What iSJhEWLQEQI electric flux through the cube? ‘3 ‘3 A) 0 ”249’” No K“ Mm: a» a . 2 N mZ/C ‘" K, 3.) M M‘? ‘2: V}: ngi C) 3 NmZ/C S 0 C2: r“ ,{ m 5 D) 4Nm2/C fl . ‘i‘jg‘b LION/U SOY S “'3 UV M32. 11. What is the total electric flux through the shaded side of the cube? A) 0 NmZZC. M ,9 C [ m '”' if; F e : o B) 2Nm2/g:> Q L~ A 3/31 4’) A/ @/ O ) Rojéfififvc : 2? IS A "\ D) 4Nm2/C /C/ ASIMQ’ A IS im 2 M A g 5‘ E) 6Nm/C _/ Q ngé X'OV” L, 12. What is the magnitude of the net force on a dipole in C __ d‘ {Tc/h 0% a uniform electric field “ti/ow +6? W, C ‘ 65k") ‘ "'3 i“ 0 )ZQE [ l v ) D) QE sinB DC) *WV F l g V) 0 E) 2QESinO if? ‘51:» 3‘ ’- .~_ «a . ”"W m I ,—. . 1, J“ ‘ r ‘4 x, . .14} Spring 2010 )(‘i tr} 4' 5 U" m”) i“ “ 6’ $59 . . First Midterm The next 3 problems refer to the following figure. An insulating sphere has a radius of r; and a net positive charge of +2Q uniformly distributed through it. It is surrounded by a hollow conducting sphere with a net positive charge of +Q and an inner radius of r2 and an out radius of r3. Conducting shell Qm=+Q 13) What is the magnitude of the field at point D, which is inside the caggiucting shell at a radius of m ? c K A) S “EM/(£04m?) C) 2Q/(804TCI‘D2) D) 3Q/(so41rr02) E) Q/(8047E1'D2) ,LVW S) d)? C? (‘ 0/1 Ci {J 1,» 4,0 V , “‘- f P?) G \\ WWW -t.\ 14) What is the charge on the inner surface of the conducting shell (at radius r2)? d / // A) B) 2Q C) Q D) —Q E) -2Q V/Ms.w,,--—w 0 ‘ Al {JOVW D} E: O \ 90 Ml C We (86’ (Ox/lialw'ai \flgldip 0x (mggggflfl QJVVRO‘? ’Ww’WflM D :;O . 30/ thew -‘ S 7 QC? m M MAW SW‘ C” 15) What is the magnitude of the field at point A, which is inside the insulating 5 here at a radius of W,R%QYM\'3 C m (if (imam "" ‘flm’e ‘- 53 3 C “1&5” VB) ZQ/(8047U’12) C) 2Q/(eo4nrA2) D) 2QrA/(8047rr13) UN 3 ’1‘ E) 2QrA3/(804atr15) N H : 2E M toga" 5 d s. n+- , emcl i ‘leum,of " Q is” ’71 ”WWW, N w§‘Q;/\ Sz WE] CQ \ _ 7’ 2G 0;? mm“ __ g 'g %Tr3 E. A r- &' ‘HTrA = 50 FF S7 , 269m ‘2 a“ SpringZOlO aura} 0 ' E1.6 V1 First Midterm \mx r13 C701 u<._s’\a\/\ 5W颀 W-\x FIR TLon AnwrPr 1m 1 oints: A piece of an infinite charged wire is shown at the right. The wire is positively charged, with linear charge density of 7». It is surrounded by a closed cylindrical Gaussian surface that passes through a point P, that is a distance R from the wire. a) For a positive test particle placed at point P, what Gaussmn is the direction of the force that it feels from the surface positively charged wire? .1 ....................... _ " """""" (ipginMrclepng: zero, towards the wire, ' C away from the wir’eDarallel to the wire, \MAM L P (1 point) Ex lain our answer Charge per unit (32” length on wire = A b) (3 points) What is the total charge enclosed within the Gaussian surface, if the charge per unit length on the wire is H»? Cindi/9;? ewefgwf 3" >\- from M c) What is the sign of the total ical flux through the closed cylindrical surface? (1 point) Circle one: zero, positive negative (2 points) Explain your answer ’ £3 . _ ’m 4 .//;. r s ' , , i t/LC’: )L/"f -- ”39$ {1 Via if"! if 'i ”C / P6393, 5+ 5 f <3 i, if if"! } '5' Q Spring 2010 El.7 V1 First Midterm d) (2 points) The cylindrical surface is composed of three parts: the circular top (1) , the side cylinder (2) , and the circular bottom (3). Draw the area vectors for these three surfaces. For the cylinder, draw the direction of the area vector at point P. l - Top 2 _ Sides 3 - Bottom e) (2 points) Do any of these surfaces have zero electric flux through them? If so, which ones? , \l/{s "WV H”, l 3 ”O P W wit/VWM '73 @‘l‘ . ~22 ' ' S \YWCQ. E, '13 (I ”to A V f) (3 points) Using Gauss’ law, determine the magnitude of the electric flux through the closed surface due to the charged wire. Express your answer in terms of so, 1:, L, R, and 7». flex : emcjm: >\L, 6:0 60 Spring 2010 E1.8 Vl First Midterm D nAnwrr i Consider the following two arrangements of point charges fixed in space. Is the magnitude of the electric force on +q due to the two +Q charges in case A greater than, less than, or equal to, the magnitude of the electric force on +q due to the single +2Q charge in case B? 1 l f, (a) (1 point) Write greater than, less than, or equal to: (f S; All/ML? VA‘ (b) (4 points) Carefully explain your reasoning. Please be sure to include ALL reasons you can think of: TWO EQRSéi/ts" ‘" fm A Mae Particles have at Sll‘awl'lg {git/WWW d-ietamce {row m m +7) (Marga ‘ l F d (:5 P 94 , 7/ a Way ' mm 376% wee, / S .. j“ A m WY’H'OX‘ COMPOMM‘S are Fish/t9 <3 {MM Mor‘tmwd’al (oWOMWFS aw $53691 Tm vet/'45? ea ft) M” tars Faucel (Mk I SO 5?“ re derrmeetl if; [m9 Spring 2010 E19 V1 First Midterm Now consider a third arrangement consisting of the +9 charge with a charged insulating rod having length y and charge +2Q distributed uniformly along it. Rank the magnitude of the electric force on the +q in case C with that in case A and case B. [ For example, if you thought the force was strongest in case A, with B next strong, and with C the weakest, write A>B>C. ] e > a, >, A (d) (4 points) Carefully explain your reasoning. Please be sure to include ALL reasons you can think of: A is); C if?) WC?“ ”h“? f?a§cm‘= CXWQWWM hA b. (c) (1 point) Your rank: in C/ KW avfl/ng flgtad’ama beWmn but erlVV *WM A4 4M0 “W1 C;/lW1 A} MM Faki \‘3 Véduqég 3:95 at (as (At/8&3. But/1w C X142 QWVfing “file ’15 <6)Sd Spring 2010 El . 10 V1 First Midterm ...
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