251sp10exam2soln

251sp10exam2soln - Questions(5 points each Please answer...

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Unformatted text preview: Questions (5 points each) Please answer each questions by blackening the letter of the best answer. Q1 A power line carries current to the South. An electron 10 cm above the wire is traveling to the North. What is the direction of the force on the electron? 5 , - a) To the East e) To the West l/ (9 j; b) To the North i) To the South ____,____———?—~ c) Straight up a Straight down I u/ ‘23 E d) Zero 7 ‘9‘” A) é—T? 5 Q2 The circuit shown includes three identical A V’W’V light bulbs, a battery, and a switch. All circuit elements may be considered ideal. Initially, it is operating with the switch open. When the switch is closed, which of t he following changes will occur? a) Bulb A will get dimmer . Bulb A will get brighter c) Bulb A will stay the same d) There is not enough information to tell Problems (30 points each). Please show your work and circle your answers. Missing or incorrect reasoning will earn no credit. A 7' \ P1 Six ideal resistors and an ideal battery are 359 M \ connected as shown in the figure. I a) Find the current through the 35 Q resistor. 30 V 10 9 b) Find the current through the 10 Q resistor. 20 Q c) Find the power dissipated in the 50 Q resistor. / k / \ T A 12-11 gym/Me M} l 96A 15 5 , 99-2. [a UL 1,9??? ‘3c9—- 3677‘ ~57”; ’0 QB 14 w. WMA: 7o~ 9517, " {002"13220 :27 w — $57; T 579g x?” 7'0 aqua/w (”V (gov-[2.01, :0 ——__—_—p T: 0.94 "’l a .~— )pe/f flue Wok W70 0*) 4,0 3y(os7»s\oz; fif b) (9, L977 0) FZILK 1 (097713"? : 1/25“ w :55? P2 For a long period of time the switch S is in position “b”. At t — O s the switch S is moved from position “b” to position a After a long time, the switch is returned to position “b. ” Please find each of the following. a) The current through the 1 M9 resistor just after the switch moves to position “a. ” b) The current through the 1 M9 resistor at t = 5 s. c) The charge on the capacitor just before the switch is returned to position “b.” d) The current through the 1 M9 resistor 10 seconds after the switch is returned to position “b.” a? U/Uéé’lflbcrefl C 54:21!) To Tffifldl C/flCUI/ § 7‘7 I K, b) A5 ofl/fl/rwé o/M'ACzés/ 13%6 «a: “1/1/10 5/ l 0) /fF/'i4 Lax/6 77/76 CHM/5 5W5 49=14¢ = {VI/0 c at“ 4'5 (”max 1794 y/s CMAW newer gar/y ,357/5/794; [/V ”/4155 1/: a - If ‘r P3 A very long copper wire of radius 5 mm carries a current of 200 A. The current density is uniform across the diameter of the wire. 4',- 5mm / , 5 ___._._—————-——- /—————9 Please determine L‘ a) The magnetic field a distance 3 cm from the axis of the wire. b) The magnetic field a distance 2 mm from the axis of the wire. c) The voltage drop across a 1.5 meter length of the wire. The resistivity of copper is“ ,\ 1.72 x 10‘8 92m 69 (9&7? (05 P4 A coil is wrapped with 149 turns of wire on the perimeter of a square frame of sides 23 cm. Each turn has the same area, B ® equal to that of the frame, and the total resistance of the coil is 4.93 £2. A uniform magnetic field is turned on perpendiCular to the plane of the coil as shown. The field changes linearly from 23 cm :3 L 0 to a final value of 1.35 Tin a time of 1.19 s. 5,4 A t Please answer each of the following questions. a) What direction will current flow around the square? b) What is the flux through the square after the field reaches full strength? c) What is the magnitude of the induced emf in the coil while the field is changing? (a) 5 pure Wvémpwm/flcy 77wqu 5 (pr/7&F Are; 771 ccw Constants R: 8.3145 L m-K NA =6.02><1023 R k3 =——=1.38><10‘23 A e=1.602><10‘19 C l k: =9><lo9 472380 T. llo=47r><10‘7 —m- A c=3><108 3 S me =9.11><10‘31kg mp = 1.67 x10” kg Force, Field, Energy and Potential fiqu AU 2 qAV nfzbfiai E=—VV Point Charges fi q" Ezk—r r2 V:kg r E=jk§f§£ _ ill V—Jkr pairs Formula Sheet for Physics 251 Flux and Gauss’s Law ¢=ll5wm gDelosecl = QBZLOSed CaQacitors C22 V CT = is parallel l l — = ‘— series 1 CT C .- Q2 CV2 = — 2C 1 2— V 2Q Current and Current Density Ohm’s Law Esz V=IR Resistivity and Resistance Electric Power P=IV Real Batteries V=E—h Addition of Resistors RT = R1+ R2 + series : i + —1- + parallel 1 RT Rle Kirchoff’s rules 2100]) V 2 0 21mm?! 2 0 RC circuits {charging} I = Iie T wall—J] T=RC RC circuits 1 discharging) I I=Iie T Q=Qé¥ T=RC Magnetic Force and Torque quixg d"=1dixl§ tzfixB Egg Flux and Gauss’s Law for Magnetism (p: jB-dzz (pclosed = 0 Sources of Magnetic Fields B = & q17 >2<f 4717 r E: £1511 2x? 47E r I IB[ 2 Hi center of loop 2R Ampere’s Law §B ' di : “0(Ienc + 11/) where Id =80 dt Faraday’s Law l , i l l l i . l ...
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