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sample1.soln - Student Name Student number Multiple Choice...

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Unformatted text preview: Student Name: - Student number: ___ Multiple Choice Questions (3 points each) Clearly circle the letter of your choice; you do not need to show your work. No points will be given to questions with two or more choices marked. No partial credit will be given. 1. A ping-pong ball has a weight of5.0 x UTE N and is covered with a charge of 4.0 pC. What electric field directed ward will balance the weight of the ball? a. 8.2 we2 we 6.2 x 10“ NC 0. 2.0 x 10‘7 NC d. 5.1 x 10" we 2. Which of the following best characterizes electrical conductors? at are always uniformly charged bfpotential varies on the surface @electric charges move freely daexpert on electric musical instruments 3. The beam of electrons that hits the screen ol'a TV is moved up and down by: a: moving the electron source. b. a phosphorescent coating. 2: varying the electron’s charge. ®electric field between parallel plates. 4. Object A exerts an electric force, F, on object B. Object B has charge q, and object C has charge —2q. Object A will exert what force on object C? Assume the same separation distance in each case. a. F, opposite direction as for object B b. 2F, same direction as for object B c. F, same direction as for object B @ZF, opposite direction as for object B 5. The plates of a parallel-plate capacitor are pulled a small distance further apart. How does its capacitance change? a. increase .decrease 0. remains the same d. None 0fthe above 6. Ifthe distance between two isolated parallel plates that are oppositely charged is doubled, the electric field between the plates is essentially unchanged However, the @ potential difference between the plates will double. b. charge on each plate will double. c. force on a charged particle halfway between the plates will reduce by half. d. force on a charged particle halfway between the plates will become four times smaller. 7". Consider two charged spheres, one with charge +2 C and the other with —2 C. A proton is at the point halfway between the spheres. What is n_0t zero? a. the potential energy of the proton b. the work to move the proton from infinity to that point @the force on the proton . all of the three above are zero 8 If the voltage across a light bulb is doubled. what happens to the power dissipated? Ignore the change in resistance due to a change in temperature. a. It doubles. .lt quadruples. c. It increases by a factor ol‘2m. d. It increases by a factor 01‘2”. 9. Two cylindrical resistors are made of the same material and have the same resistance. The resistors, R. and R2, have different radii, ti and r2, and different lengths, L1 and L2. Which of the following relative values for radii and lengths would result in equal resistances? In 2 [‘2 and L1: 2L2 b 21‘] = 1‘2 and L] = 2L; 13’. 1‘1 = [‘3 and 4L1: L2 @ZI'I = r2 and 4L| 2 L2 ll]. The Eistiflty of a material is doubled when heated a certain amount. What happens to the resistance of a resistor made of this material when heated the same amount? I doubles. b. It quadruples. c. It halves. cl. It stays the same. 9 .. 5| ,1; ..{u‘ Student Name: ; Student number: -—_ Problems You must show all your work and use correct units for numerical answers to receive full credit. Use the back side if needed. No credit for writing down equations only. 1 1. Two identical charges (q = —4.6 uC) are placed along a semicircle of radius 3.0 m, 30" above the horizontal, as shown in the figure below (points A and B). (a) What is the resultant electric field (magnitude and direction) at the origin of the . coordinate system? (7 points) (b) if charge q] = —6 uC is placed at the origin, what is the electric force (magnitude and direction) acting on this charge? (7 points) (c) Consider the two charges in (a), without q] at the origin. What charge (12 (magnitude and sign) should be placed at point C so that the electric field at the origin is zero? (7 points) Ezlfl r EA JSQ‘ixth m c (iéxlO‘SCi (3.0m)‘ 45949 Nlc would A-cé E3 = [mean mm; 4,991qu Q4- 4594.? mic toward 8 (3-0 m)’ _L, _.o. Crease” X4414 ‘0 CSIan’) (45‘34 ‘4 ) CO; 50 “X45140 CS‘mBo") (4594. ‘ll _._ ___ .- .._.._.. __w—H—w firiffiWfiefif) 4‘4 4 m .\ lEM’t = %§EWNIC_£fwa.rd _ Pain1 C“! / 6??) WWWH—mm.._¢_ .....,..___r F : 236 x {O'ZN— POEM 'U’) ‘HkQ OPPOSHQ direction OF truer Pomi down H19. [1132 ,away {(007 POW C Hum—Mm 4444+] ‘ _ WC? 9M: 4 4 NOGomji "“1 _ Tifi‘ix[OCYN-mi/C2 @9/ 12. Charge A (2.0 C) and charge B (2.0 C) are fixed on the x-axis. Charge A is placed at x = —~2.0 m and charge B at x = 2.0 m. (a) What is the electric potential mid point between them? (6 points) (b) Find the electric potential at x = 3.0 m on the x-axis. (6 points) (c) A third charge is moved to the origin of the coordinate system. What is its charge (sign and magnitude) so that the electric potential at y = 2.0 m on the y-axis is zero? (6 points) (d) What is the energy needed to move the third—charge from infinity to the origin? (7 points) ‘ a Vat; VA :_ {9.94 x I07 N-rnJ/c’ 20-06) 2.0m A we 03 ' 3313c VA:- SFiGlXqu VoHS 63' ® ' VB = W : 239x :0" volt; 20 m . V-rotal = VAtVB 7- QCSR‘inOl UoHS) 2‘ ’79? XflVoHS. 9- 1 VA: MM MOC'N‘WC’ (3-0.9 = M?“ 10“ use ' e mam 5.0m 1 Va: (EH ‘lxtO‘1 — ’ c’ 2- : migx ,5me 5m thVAJrVB 3.5% X to“ + L795?! 0'0 watts 2.!576 X l0m .Hs. .6) - (/~l\ __ T: ixzt—Y’ : ,1” 4— 11 : 2.82? m _ 2 ._\ afig - . 7- if .t A C 2 a VA - (W? X IO.N:m C )(2-06): 6.36 X ‘0? UDHJ. . 23:18 m. VB = VA : (9'9. x (l .m’lc’ 2.0C’ : 6.36 Xqu VoHS 3‘929m' \/A r V; = 2 [6.36x 10"): (.272 xlo‘° Vol-Lt Vat" VB ‘l‘ VC :— 0 v“ Vs = —vc {KM} 59 A'PE= V% '[VAefl r 2 {Cg/I'l-flledowm) (3-0m KG ((339 X IO‘lN-m’kj APE M W a“) i : 07?? X (0'0 VOHS) (“-295 C) : PEA + PEB: 2 [fig-12052.0CJJ A =__,. ' 0 l0 ‘ PE 5 8331} x10 3’ C9 7/ 13. A 100 W light bulb is left on for 24 hours. (a) What is the electric-a1 energy used up by the light bulb? (6 points) (b) in the US, the voltage in the power outlets is AV = 1 10V. Find the current that flows through the light bulb when connected to a power outlet. (6 points) (c) Find the resistance of the light bulb. (6 points) ((31) Find the charge that flows through the bulb in 24 hours. (6 points) p:|oow, i=24h' 3999i: 864003 lb 9 E 2 Pi: =Qoow)(8640083= S‘s 64xzo‘ J b) szllov p: IAV ___ I=_lo.mr_iQO_\/\l.__.__: 040? A / A HO V :1 Z‘ ._______._....-;—__ 2 J1 R 1‘ 0309A I) d - AG J 1'71? AG. : I Ail: ': (0907A).( 864008)/ Q2Z85X lOlLC ...
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