sp10test3s

sp10test3s - Student Name: Student No: Louisiana State...

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Unformatted text preview: Student Name: Student No: Louisiana State University Physics 2102, 6:00PM Thursday April 15, 2010. Please, circle your section: 1 & 6 (Giamrnanco) 2 (V ekhter) 3 (Rupnik) 4 (Bowling) 5 (Rupnik) - Please be sure to write your name and student number and circle your instructor above. - Some questions are multiple choice. You should work these problems starting with the basic equation listed on the formula sheet and write down all the steps. Although the work will not be graded, this will help you make the correct choice and be able to determine if your thinking is COI‘I'BCiI. - On problems that are not multiple choice, be sure to show all of your work since no credit wtil'be given for an answer without explanation or work. These problems will be graded in full, and you are expected to Show all relevant steps that lead to your answer. Note that you can often do parts (b) or (c) even if you get stuck on part (a). - You may use scientific or graphing calculators but you must derive and explain your answer fully on paper so we can grade your work. - Please be sure that all numerical quantities include appropriate units. Points will be deducted if the units are absent. In addition to magnitude, vector quantities must contain sufficient information to tell us which way the vector points. - Feel free to detach, use, and keep the formula sheet pages. No other reference material is allowed during the exam. 0 The only electronic devices to be used during the exam are standard or graphing calculators. All cell phones should be turned off and put away. Cell phones are not to be used as calculators. Any cell phone heard or seen during the exam will be confiscated. ' May the Force be With You! Question 1 [8 points] Ta k 4371 L (9w? 6, PA Cg all") C 6 am The figure below depicts four identical wire loops lying in the plane of this paper, each carrying identical clockwise currents, I, as shown. Each loop is located in a region of uniform external magnetic field, B, in the directions indiCated. The magnitude of B is the same in each case, only the directions differ. 9MB I we CW/ tic/<6 1'59 fieflmwg 7L0 Hme [cap as i3? I'D/cg” E + . o + 7 Do —> 59 ® @ B@ 60 9 Cl B 0 @fioo I 19/ I I ® ® @ © _ (a) (b) (c) (d) "'2) I I + s (9 IS nag/e [Win/eel“ 3 m0/ [751me (“GD/:3; ‘ i) Which loop(s) experience the greatest magnitude of torque due to the external magnetic field, B? e g g {ti/fXB :[flgwcgjw 50 WW7! fwéce tar/L944 (9: ?0° is (d W961!) - ii) Which loop(s) experience zero torque due to the external magnetic field, B? 7,3; M) wLw<9300 flxfizo 29(le e M iii) Which loop(s) have the least potential energy due to their orientation in the external magnetic field, B? Note that a negative potential energy would be considered fie smaller than either a positive energy or zero energy. 34% Qfluf ll fun/1 mdlfl‘m .6 Cb) (c) (d) *9 m I‘Yl {W W“ be" WW 7) :' Pct/m [/ej 7L0 B :9 [710% [1 [~me [UL ,‘5 cm7ll~Pfiw<t/C/ 7L0 Problem1[17 points] acpqp+€d ‘90”?! HW 7/ #12 The figure shows a cross section across a long solid cylindrical conductor of radius a. The current density in the conductor is directed parallel to the axis of the cylinder, and is dependent upon the radial distance, r, from the center according to the relation J 2 fir where J is in amperes per square meter, and ,6 is in amperes per cubic &, meter, and 0 S r 5 a. f" b 4 Obtain an expression, in terms of 5 and r, for the current flowing through a cylindrical portion of the conductor whose radius, r, is smaller than a. lineage amt MA; I“ h. ’79 ,‘ m1/91+00flfi r r What .101?“ Aqu 2mm; jg X3,” ’ Weft I J 7% oétf‘ii : o ' '0 "’ 3 ’1'“ 9% Use Ampere‘s Law and your expression for the current from part (a) to obtain an expression: for the magnitude of the magnetic field, B, at that distance, r, from the center. mm l0“ 5 @343 W122 Us? Tam outage @8044 : HM alga?" :2; Brflfi F2. f 5% Use Ampere's Law to obtain an expression , now in terms of 13, a, and r, for the magnitude of the magnetic field at distances, r, from the center that are larger than a. 3 ,_—. 7001— 1‘70») ,L: fi’TTfl riot?“ 1“ fia 1v) Make a sketch of the magnitude of the magnetic field, as a function of radial distance from the center, on the axes drawn at right. flgpc/ Dlrec-hbn‘s,’ RH]? Question 2 [8 points] flaw; E’C/q Pa'vni‘ i 1 Ch 2 fi 8 i The figure here shows three long, straight, parallel, equally spaced 9);? wires running perpendicular to this page, with identical currents either into or out of the paper as indicated by the dots or crosses. 8C 'a b c ank the wires according to the magnitude of the force on each due to the currents in the other two wires. Rank fro: greatest force to least force. 4.53 E % a=b>c use :1 “F : X B b>a=c deg—HA? cflweuiwfi 0M0?! ' £19,“. +Ucles Op my: 8 c>b>a OS ail/{awn diam (b) expeniéucfi “(5W0 “57140123 ” fmces +0 7%? AghL clue +0 flaw #544ng Piggy”. “ WEQk.“ ijCe 0% exPQwQMces CL: weak" an ix 6%”T5” terse] aur- 1h oppasri‘c citree'i‘ricms ii) Which wire(s) experience a net force directed towards the right? Ky onlya (a) 7497i 990% ,‘3 T on] b - b 8:: Quad [6,) V1 9+ 38f QflG/ 1 5 - _ fl“ "‘23 ~——-a Q 056’ jC : IQIB mud fight}? (a) may” (a) pxpmrehcé? Aghiwwd J%c€ Problem 2 {17 points} 7am” (g In the figure at right a 20 turn coil of radius 4.0 cm and resistance 10 Q is coaxial with a solenoid with 50 turns/cm and radius 2.0 cm. The current in the solenoid increases linearly from 0 A to 50 A in a time interval At of 15 ms. i) What is the magnitude of the magnetic field in the interior of the solenoid at the end of the 15 ms interval? 5"? BSOQ 7; Pol/1i : {Fojégtfih %“){5‘op) iffl/l / ii) How much magnetic flux (magnitude) does the current in the solenoid produce within the interior of the coil? 63?} a : fill? a Wes m H iii) How much current (magnitude) is induced in the coil during the 15 ms interval? K“ fl 4) ¢ ‘ fl _ 3,9 we 77- a O 1 9/07/57 *N/ 4+ "NZ? : [If-:f” 075“ ' u 5 3 V iv) Annotate the figure at right by adding "x" or -" as appropriate to indicate the direction of the current which is induced in the windings of the coil. Be sure to show direction both on top and bottom. Explain the reason for your choice. 6 . ,- ' ‘ hmeael l" 5/14 C? so!“ I S I J {3) 7/“? M0! +0 fix? Atgk'é'j euflflw+ 50A in cc)in havle [Mach/cf 9/12): “[0 leg—F (in; ole/">052 Chat/‘61? Question 3 [8 points] An ideal inductor consisting of a solenoid coil of length (3, cross section A, and turns per unit length n, has been drawing a steady constant current, I, for a long time. If we then doubled the number of turns per unit length in the solenoid but kept the current, I, cross sectional area, A, and length, 8, the same, then waited again for a long time, what has happened to (i) the magnetic energy stored by the inductor 3‘0. 099% 3) 1t remains the same b) it is twice as great as before c) it is half as great as before d) it is four times as great as before e) it is one—fourth as great as before M? (ii) the voltage drop across the inductor b) it is twice as great as before c) it is half as great as before d) it is four times as great as before e) it is one—fourth as great as before 15m. : fianlflj' l"? KL jg gawk/ed) L 6960m€$ GS JMUCLL Problem3 [1713mm] 163W HW Cr # 7 A coil with an inductance of 35 H and a resistance of 1000 Q is suddenly connected to an ideal battery of 180 volts. At the moment exactly 35 ms after the connection was made... i) At what rate is energy being delivered by the battery? ii) At what rate is energy being converted into heat by the resistor? “2 a; if»? :(tueYC/owfi) : IQJ W F //—\ W iii) How much mtg} energy h: the battfiry delivered during those firstggsgljs? fl 0 35.5 : \S‘PBfiTTCfl :j(\/snrr\ J’(fl : jég’ov)['/8pr(l d e ‘9 o . 035‘ 5 2 (3-37 M) 50w“me : sad/<52 J O octaqpie‘i/ HW’O ' #3 In the figure at right, the switch has been in position a for a very long time, and is R v [I + a Question 4 [8 points] thrown to position b at time I = 0 s. i) Just the tiniest moment after the switch is moved to position b, the current Pt “3 3338 m Capone. had hem e)2V/L Chwépo/ +0 V [Jule Hie Lut‘i'k SW’LCK Swi‘i‘ci’t W08 51L “CLIr Ct'tL “13 [MIN/M +A€ SW,‘I‘CL\ mot/63 iv “A L we! C 714w choci‘le 4416‘s 7L0 kqvfl d,5cl]wé:ll:|5 [4 EU; Zr say/1‘8 + Lw/i malL (ct/low Gm 1h57LQM+q”QWS (mm C M comm»an L’s (wane/ML WQS 0 {997039 +A€ StufiLcA I: ' H H 30' ref/i A9?“th 0 «M5le Q707£€a ii) After the switch is moved to position b the current in the circuit will oscillate at some frequency, 3%. That frequency, 1?}, wiil be determined by the values of W a)VandRonly b)R andC only / u. . dLonly 12 V ewe}, Q N OWL a' _ , ,only ft‘F CinCUWL how f)R,L,C,andV flotqmlee/ 70mm #WIO air/OWN {aka City‘é‘ct‘lbws v.1; A Problem 4 {17 points] 0 g SW 100 (6‘ V96 ; d'fl r a 5 00+ LuCt Kc] A Gaussian surface is in the shape of a truncated cone. The bottom of the cone has radius 20 cm and the top has radius 10 cm. The height of the cone is 30 cm. A magnetic field of 250 mT is constant with time, uniform throughout space, and is directed upwards, passing perpendicuiar to the top and bottom faces of the cone. To specify flux directions, assume flux pointing out of the Gaussian surface is positive. i) What magnetic flux passes through the bottom of the cone? 2— x0) j?) 0? F} __ 6 H [80” —- (2 ,.._-—- 7 _ o H to; I , 6 J H . 2 M 4‘9 av; €01“: QET 607T ) 6 J ( ) :‘SML/XIO'L T“. m1 a; Wot direct/m ii) What magnetic flux passes through the top of the cone? “2” do : {€473 .—. MW, :éwdérrwmfiw" To! f"- ___3 B It If M :1—7, 85x10 [.ML 1/ means w? //-—-\ iii) What magnetic flux passes through the sloping sides of the cone? 3:6 U}? 31h”) ¢7~op+ BH‘T + 3:DE5 f O ' ~— "3 "L ‘2; smes : aflopflégm :: — 7,85 >U0 Tun - -S./V>UO pm -_ t ‘ ’1” L \\ l; r“ “I” Q-HX/O /'m [earl/wad) ‘1“ iv) Would your answers for (i) through (iii) above change is the cone were made twice as tall? Explain. 6?} HO "' $70? @3077— ”flz CLAW ,__..—-—- __'-""" 50 «316/6; fiat/“3’36 5W ¢7DP+ 307777.: SIDES : O ...
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sp10test3s - Student Name: Student No: Louisiana State...

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