p240f07_mid2_sol - Physics 240 Fall 2007 Exam#2 Please...

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Unformatted text preview: Physics 240 Fall 2007: Exam #2 \ Please print your name: L) (Egg g9 W l\/\ V\ Instructions Fill in your name above This will be a 1.5 hour, closed book exam. The exam includes 20 questions. You may use a calculator, please do not share calculators You may use two 3”x5” note cards with notes and equations you think may be useful. You can write on both sides of the card if you like. Table of constants: 80 = 8. 85 x 10‘12 C2/1\Im2 1,—— 1\ * .L/(47t80) 12161661101: 1.6 x 1049 c qprotonzl 6 X 10-19 C 1ne1 lemon“ :9 1X 10—31 kg 1111010101.: 1.67 x 10'27 kg 110 = 47E X 10'7T1r1/A2 G: 6. 67 x 10 ” Nm H/kg Version 3 Page 1 F 12.4%, M (’3‘ 1. Two charged particles of equal mass are traveling in circular orbits in a region of uniform, constant magnetic field as shown. The particles are observed to move in circular paths of radii R1 and R; with speeds v1 and 122, respectively. X X X K X X K K F...» M: E ,‘h‘-- «o *3: UK“ a/ ‘\ pun—t r ‘3— X x X \x x / >1): 3»: w ’ . " ,_ {g 013:"!L 51% \R1 l [IR % QB E“ W iv 97‘3" ”*3? \ \r‘ \M "V8 2: 2’9“be iQ-Fv :1 t , *— 3 W... t x X ‘1!“ x x x i: x it" . f g f“ E . - . . if i As the figure shows, the path of particle 2 has a smaller radius than that of particle 1. if m ;m E ‘J . ._ l 5 Which one of the following statements about this system is FALSE? i ,3 E 3“ A) Particle l carries a negative charge. i “~- J” E IVI/Qil < lV2/Q2l E The particle velocities have no components parallel to the magnetic field. 5'5; 1‘ D) Particle 2 carries a positive charge f “w E) iv either particle gains energy from the magnetic field. it; gr (3(3) ta 2. An alpha particle of charge +26 and mass 4u, and an 160 nucleus of charge +86 and mass 1611 have been accelerated from rest through the same electric potential (lu=l. 6661x10~27 kg). They are then injected into a uniform magnetic field B where both move at right angles to the field. The ratio (of the radius of the path of the alpha particle to the radius oi the path of the nucleust is ., A) rat/1’0: 1/2 W B) Iu/ro ~ 1/8 E IC) Era/1’0: l/l (1H Viki \ffii fié’j {Al iii-“xx Iwa/ro 2 1/4 . ( l i ”a m “\i/ .\ E) None of these is correct. K M“ W: v «— (i \X {I Veision 3 ‘i"Page2 \ w W imfictw \‘ "N. ace... 3.: All” r- : (n. 43W“? ,/ Use the following to answer question 3: C‘JECL 2' “WMWMW 3. You connect three capacitors as shown in the diagram below. If the potential difference between A and B is 24.5 V what 1'3 the total energy stored in this system of capacitors if =5.0nF C2=4.0)LF andC3=3.0nF? iii? 6. 8 X 10 “4 J B) 4.0 X 10‘4 J C) 1.5 x 10'4 J D) 2.2 x 10‘5 J E) 1.7 x 1043 Version 3 Page? t” “tum C38 “f: Use the following to answer question 4: All four resistors in the network have the same resistance. R1=R2=R3=R4 M 3:» u “E: E: 3: in?) {at “" Cf ““ W r“; K cf r: 4. Resistor 2 IS removed from the network, leaving an open circuit in its place How do the currents in the circuit change? 1;; {3 3.3? $4 an em: wa‘é A) Less, current flows through R1 and zero current flows through R3 and R4. B) More current flows through R1 and less current flows thr ough R3 and R4. 33 ‘5} tar; 39} e; a? C) The current through R) and the current through R3 and R4 remains unchanged m Less current flows through R1 and more current flows through R3 and Du; . (:3; £23 1 3,3 .L E; E) More current flows through R1 and zero current flows through R3 and R4. * Li (7; K Q; cute {Muir {midi—1‘ Um £493; Q‘ Cixfi £3er E?" sad 6% a wwaWwW/MWMWMWMMMW ‘ ,, “W WWW “ f‘vfl * f'" M If 9‘ f N .t {mgr k is a ”a M We firemm Mflug “9W “N Version3 Pa e4 i ‘ g i » EFL f \ g fewer“ ”be £fi{ carpi/1 “ff Q53 5 a?“ {:29 NMMNN“ W ‘zjer ‘5 Q "fli‘ R4; I firm/(3% {93¢ flung {stander r242: mm 2,, Use the following to answer question 5: E D {@03ch m Chit) an A 3331\ WT fir-[Y f if PFDMQM,‘ 9932”. 4%) A (A n Kflfifi 2 z ’i A. m A an - X A A A 7:er 5’ (a The four current loops depicted have identical dimensions and current. There is a uniform magnetic field in the positive y direction that acts on all four current loops. L ‘x. - “A A” 5. Which of the current loops nas the larg‘st potential energy? A) a m an w. a is"? (I? ‘0 U M ”3’ is) > 0 [Egg d ”l i E) they are all the same E‘j file '1: C: ’1 «£94 "K I“ 801%"? j (5516.3qu l3 JSQE “will" [C @33‘1 [£36767 Q3 : Ii” 4“ 1/ we}? 3' (km w w (% Version 3 Page 5 Use the following to answer question 6: A long, straight wire carries a 10.0A current in the +y direction as shown in the figure. Next to the wire is a square copper loop that carries a ZOOA current as shown. The length of each side. of the square is 1 00 mi ‘ , kw it e U9 4WF I)“ :3: 3 AM {0 B I: A“! 3 :rr E as T“? 4"“ 3.3 “I: r - ”’ ‘ .3? xi Q5 m SEW L f‘ in? L \1'6‘: \ 5 rat is the magnitude of the net magnetic force that acts on the loop? &V\ :5“ w @1.7><10’5N i B) 1.4x10'5N C) 8.0x10'6N D) 2.3X10'5N E) 1.1x10"5N A portion of a Circuit is shown, with the values of the currents given for some branches. What is the direction and value of the current i? A W A) l,4A B) t,2A t,6A f“ D) t,6A t t; E) t,4A \h g "a; tttttt as \e a a A "t " r: 3 A gwgrw“ a» .,,,m.~.~~-‘ L ”rift“ W M Q it ‘t E 2: j a“: ‘3 Di 2. 2+ g E: - 1 Version 3 Page 6 Magmlé‘e Quid (an «giants, (that? Carms in» (“Lia Nixie)» 5:; M £52 fire [69? (”barf-”t "*3 flaw 21:3 ,3 KCrmM Q carriers wad lgq @2353:ng The rectangular block in the figure is in a uniform magnetic field, B. The current I is flowing perpendicular to surface 1. If the electric field in the block has a component that points from side 2 towards the opposite side of the block, then which of the following statements is true? A) The block must be a metallic conductor. B) The charge carriers in the block are negative. C Positive charges accumulate on the side opposite 2 . I D The charge carriers in the block are positive. E) None of the above is true. . The magnitude of the magnetic field at point P, at the center of the semicircle shown, is given by: «m Kl at gm A) PLO/132 M B) liq/27TH sfi W ? a 2 ,4 ‘ ”T? C) poi/47c]? C? 3 “" fie Emfjié :11, f D) Moi/2R {AW {1 *3 Version 3 Page 7 m at am; {2‘ 25 o 36 Q 35 o 18 Q '1“ Max ‘31 2. it. R e; In the circuit shown, the power dissipated in the 18 —Q resistor is A) 0.33 kW V B) 33 W M? g «M a; jg « a Q 47 W a}; «Q (”lived £4? "’ " S jwfifi 98 w . 1%.; 015 kW % $.— Kumfi} baféa‘iw ‘4 " 3} M i ”big a” {‘3 Mr; 5 s {a r IL ““ L ~yefia at awe t0 ”(W J ~“~‘ 1 s 3 M .9 4“? l :2 .L ' K V W‘: "" S E a7 (21 g g fin-MN sat ”“ \i :5; m A spherical capacitor is formed from two concentric spherical shells. The inner shell has radius RR R and the outer radius 2R The inner shell of radius R surrounded by a dielectric material of /} constant K=4 out to a radius of 3/2R (grey region in diagram). The region from 3/2R to 2R 15w” filled with an (K: 1) » ll What IS the capacitance of the spheiical capaCitor in the diagram? , , A) ns R -.~ » £4 E (xvi W a; flier} gifllflfif €M?~{ C flaw” W B) 4TE€0R w ~ r” / ‘M‘ n “ @ww l4 a: Q Q 33w,“ ”M E) 327181) .RW i ”we.”,MMWX‘MWM (fit-é}, 64 u& g: i. "$3in 1 R \ \ I; a V _ l ? I .« ii: &_ m (flu \\ lg C‘fifilflériak ngmmft‘éfi'S €33 wi> \kég A Ll ”3T K (“I a V“ mm“; \ R Li“? at g \i ‘ if: A Tip“ CE 1 11".. W i g _ " Q‘W‘éé g?“ “M 'M “€n E \\ R é. /if Q a m» K WW K 5: K RTE? % i { a» M us; ”4/ “fig. ”N was» a M 3: ‘t (,x‘ i 2:. W (X \ ”I” em‘ l h ‘i I,» w 12. A certain capacitor, in series with a 720-9 resistor, is being charged. At the end of 10 ms its charge is half the final value. The capacitance is about: A) 9.6 uF - e/ , g .._ 2‘; ’B) 14 uF f _ W .. g fliC lift E :- M @me :1 r" 71;; C) L~ >3 Re; D) 7.2 F E) 10 F _. 4; v. ._ ~— “2: KW “in. 2: J- 37: l ‘ G, a Q C— a. E OK «i f i7» . m. ‘\ 13. Two capacitors arel identical except that one is filled with air and the other with oil. Both capacitors carry the same charge. The ratio of the electric fields E air/Eoil is: A) betweenO and 1 . " t . g wwl‘ii (fittiiécf/yq B)0 TL}; (Emit—3 C) 1 _ it ,- A .1 . . ghetweenl and infinity (dim g {9‘ f (‘25 3 «ELL‘QA C“ P l E) ) infinite l as K , “ r _ . “if wag Q. enema“) Ewsfir 11‘ ‘37" W... gm :3 tr“ {:2}; \ Km Eng.” 1/ ‘ c... er ”“1 *--—- 125;! if‘;{ 14. Two wires (A and B) of identical length and diameter. but NOT identical resistivity are connected in parallel across a source of Emf. If the relation between the resistivities of :2 K the wires is p A > p3, then which of the following compariscns between the electric field K % and current densities in the two wires is correct? E l {or M A) EA>EB, JA<J B , B) EA>EB, JAzJ B “T ,7 ., “2m .. l I? i C) EAZEB, JA=JB i é‘fij RM" E “L l is all (a l ’ D) EA<EB, JA:J B . z E; V I“ . EA EB, JA<JB 5’ [:3 Vfi A Vgg r: A V, ,1 m §nw AV 5pm fimfl'fi.‘ ”3W5? £22“ .. ta; 4 .7: 11 R 3 Wu. 1 t T “‘J‘ 5...... ‘2 1:“; v]\ m ° P 3 ... 34 ‘> .i (g Version 3 Page9 3A < 3‘ 15. At one instant an electron (charge = —l .6 X 10'19 C) is moving in the xy plane, the components of its velocity being vx = 4 X 105 m/s and vy = 3 X 105 m/s. A magnetic field of 0.8 T is in the positive 2 direction. At that instant the magnitude of the magnetic force on the electron is: V; Z? J” “(D M0 K i ‘WWMMmM‘g %@ » B)38XIU”N 3% M {fit 9 'C)5JX1q:N ‘Eg V_~wwww-§ E)75x1o”N 16. Two copper Wires have the same volume, but Wire 2 is 20% longer than wire 1. The ratio of the resistances of the two wires Rz/R} is A) 1.1 B) 1.2 C); 0.91 Wait/1M :2 length so may D)‘l.4 t , 0.83 gm‘ m *ei L,t2x t QMQK “A wlmmfik 22—» Q M W «M3LV‘W; Q We" ’3: “10““an I Q m, g; {LRQQZT} Us“; ‘v ”a W? i! :w in. l m, Version 3 Page 10 gwii‘cl‘ C 39365? __. actrftm‘i 0&3 {[4 “41ch r \l: (3.11) r hr. Eu gawk?“ Use the following to answer question 17: j; r; 53; Amp} 3 TQM“ \ W (infimcrl'ék f‘ 3 last} Uzi. Um! flu} if m 1an \ am E ii 3+6 17. The switch in the diagram is initially closed (and has been for a long time). What is the , M , cunent through the 6 Ohm resistor immediately after the switch is opened? ‘ “ A) lOAmps , ,, ~ ' {rift (V in B) 037Amps a EA a in C) OAmps { ,l ”l0 2 4‘ “(3(an "fi 3 . « a i D) /2 0 Amps W! {igtfiwacfi Q3342: iii/(fa: wan-bi is at W“ (”A E) 045 Amps fig i3 f» e ‘4 18. A positively charged particle is moving to the east in a magnetic field The magnetic force on the particle is toward the northeast. What is the direction of the magnetic field? A) south—east E? The situation described is impossible. . l i up 3: RE I: M Uni ”is D) north—west E) down ex“ 5; 3' él/iwiikg Em wat- a Emit W E? Vale (“Li f3 Version 3 Page 1 l 19. The emf of a battery is equal to its terminal potential difference: A) under all conditions B) only when the battery is being charged C ‘ only when a large current is in the battery I” only when there is no current in the battery E) under no conditions Use the following to answer question 20: /\ I 3,,45MI6 g: a 2; a r; a all g. 20. What is the Einf of battery l? A) 48 Volts B) 24 Volts 36 Volts D) 8 Volts E) 12 Volts Version 3 Page 12...
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