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# p240+Exam_2+Solutions+F11 - gin-O EMWWI P am SantiTicAE l...

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Unformatted text preview: gin-O EMWWI P am; SantiTicAE. l. The electric ﬁeld at a speciﬁc point inside a copper conductor is 0.02 V/m pointing to the right. What can we say about the drift velocity (direction and magnitude) of electrons (e = -l .6 x 10'19C) at this point? What additional information, if any, is needed? - A) Vdriﬁ points to the leﬁ, and We need to know both the resistivity of copper and the shape of the conductor. b3 Vdriﬁ points to the left and lay, need to know both MW in copper and theﬁgsﬁiriT}r (if m _ 72, C) Vdriﬁ points to theﬁght, and we need to knowju the resistivity oﬁlcopper. Vdrm points to thewleﬂ, and we only need to know density of md‘oile electrons in copper. we need to know the orientation and cross sectional a of the e’opper conductor to get the direction and magnitude of vdrm. E | w... _______....—.- 3:; E" :2: 7mm 2‘2ng 215:3 2. Nine identicai wires, each of diameter d and length L, are connected in series. The combination has the same resistance as a single wire of length L but whose diameter is: A) 61/9 1 a. (90 L g t __ L t : ﬂ . 2; 3: 373‘. 4:31—- M>Maéi age) m9": w) m ‘ l .w I E) 9d 0) 3 43% 3. What is the magnitude and direction of the force on the current loop in the drawing if the radius R is 1 meter, the current is 5 amps counter-clockwise, and the magnetic ﬁeld is 1.3 Tesla into page? The loop is half in and half out of the ﬁeld. (Neglect edge effects of ﬁeld) .,. 93.7 9 J A) 5 Newtons to the left 2- B) 13 Newtons to the right l jg, C) 0 Newtons D) S Newtons to the right (ﬂ ,@ 13 Newtons to the left i J 0dr) ‘\ Version I Page 1 4. A 14 uF capacitor is charged to a potential of 50 Volts and then discharged through a 180 Q resistor. How long does it take the capacitor to lose half of its stored charge? = micro= 1016) RC 7:. 7’: 1520/45. 1740 its ,_ E r 920 is Q 1 Q0 e?“ 2. ‘LQD caurmﬁmut Mae) C) 370 us D) 420 its -— N: - ms E) 300 as ' I t ; ,zpﬁg {ﬂu/is]? 1753/15 5. Two identical parallel plate air-filled capacitors (C1 and C2) are connected in series and hooked up to a battery. A dielectric of dielectric constant ic>l is inserted into C2. How does the enery stored in C; after the dielectric is inserted into C2 compare to the energy stored in C1 before the dielectric was inserted? The battery remains connected throughout the recess. 35 9w—A) Energy stored in C; is reduced B) Whether energy increases or decreases in CI depends upon how large the die ctric constant is. C) Whether energy increases or decreases in C1 depends upon the polarity (+ or -) of the battery. Energy stored in C1 increasesé-—-—'~ Energy stored in C1 stays the same 6. A yoltmeter is formed from a coil with an internal resistance of 100 Q. The meter reads full scale when 10 mA of current runs through the coil. How should you modify the voltmeter to allow it to measure voltages in a range between 0 and 100 Volts? A) Add a 1.2 Q resistor in series loo 5L IOWA B) Add a 1000 Q resistor in parallel C) Add a 7700 Q resistor in series D) Add a 0.773 0 resistor in parallel R @ Add a 9900 n resistor in series Version 1 Page 2 ~54; m 7. A parallel-plate capacitor has square plates of side 12 cm and a separation of 6.0 mm. A dielectric slab of constant 1: = 2.0 has the same area as the plates but has a thickness of 3.0 mm. What is the capacitance of this capacitor with the dielectric slab between its plates? A) 37 pF _.. 28 F 737» <3? o) 53 pF E) 16 pF 8. In the ci below, the voltage across the 0.5 mF (m=10‘3) capacitor at its . steady long term) W““Mm“www“ “MO 1052 m”) 309 r. gas-mama) ‘ ~ I w '3. 32% 7 Volts W l 2, "‘ 5.3 “VIC 7'“ 1'3 '3 9 Volts 312 90”. C) 10 Volts Va: 1 ‘1'“.5 il- D) 15 Volts E) 5 Volts 5W: 8H— VC "‘ ﬁx"; Va, 7 V W 9. A 2 m long wire of constant cross section is made up of 3 Ag (silver) length of 1.2 m and a W (tungsten) length of 0.8 m. A current of 9.5 amps ﬂows in the wire. The resistivity of each material is: 3.. E PAg= 1.5 X 10-8 Q m \ my”! mfg—{raj 3“ pw= 5.3 x 10‘“ o m 9,. *‘i’? W Which statement is TRUE? J! fail; H—A) The current density J is greater in the Ag segment.)4 "I B) The electric ﬁeld in each segment will be the same.,X i” C) The potential difference across the Ag se ment is greater than the potential difference across the W segment. 155.69 in [A (intimate-at) 3:) 7g 90 The electric ﬁeld in the W segment will be ggater than the electric ﬁeld’in' the Ag segment. E) The potential difference across the Ag length will be the same as the potential k difference across the W length. C 4:!” 4%)”ch 35,. i may» slam/WU [ f .3 7’} " ._\t. .‘ ,r" "-4-" We" Q“ Version I Page 3 10. When switch S is open, the ammeter in the circuit shown reads 2.0 A. When S is closed, the ammeter reading: 15:: 2D 2 v 9,9,1. mme 2011 J W9 A) remains the same B) doubles C) halves D) decreases slightly ‘ 36% ® increases slightly é’wﬂ 11. Four circular coils have the same area, same number of loops, and the same magnitude of current. The coils are widely separated from each other in a uniform magnetic ﬁeld given by B = 302. Rank the individual coils on the basis of their magnetic potential energy, least to greatest. (The coordinate system is right-handed, meaning 55x j) 2 2) u: Ji-B {9y ié 13\$}; gig; x ugﬁwﬁﬁl‘ﬂ’i’o M” . I u :# «.‘£0%l O (a) (b) (c) (d) ’° ﬂ 3 _ 11¢: "/42’53: VOLBDM A) (d), (a) and (c) tied, (b) JL. A. a, [W B) (b), (a) and (c) tied, (d) qut:_./H:j egg "‘ . O C (b) and (d) tied, (a) and (c) tied . (a), (b) and (d) tied, (c) 55% ) (c), (a), (b) and (d) tied Version 1 Page4 12. Four identical light bulbs are connected to a pair of batteries with small (but not negligible) internal resistance as shown in the diagram. How do the brightness of the four bulbs change when the switch is closed? (w r,va {Maid/k newt}be 2;;ch 3/ mm gﬂgm vantage Eightygxinﬁbk r” at tttzetaaatwragtr r ~ , .. ml ’ a ’ , . .-"1<f;“L4i«§!/f§i‘£ Em Mlgj‘hgﬁw ’1 3 r i F ‘ i h . “‘1 dramas/M Eilcamg'iﬁ tﬂwiﬁinwﬁl x‘Lft-ér'ri'i’g‘ 5"" 5&9” A Qantas t. Fail-aM-‘a: and B slightly dimmer, D slightly brighter, C goes out w. \ﬁB) A and B much dimmer, D much brighter, C goes out \$1- ' _ .1 1/ n f; j W C C and D go out, A and B get brighter l ‘ 5 law- E) 3 and B slightly D ingc'ligltlatrighter, C goes out gavdmtmﬁﬁ fits? , goesou,a 0 er u sge r1 er , ‘ a“ IﬁdPg-‘%’I*“‘lﬂ? *{ﬁ‘l’i' f} PM}: ‘5‘" . A’ } gird-Egg? targets} . 13. Electrically neutral salt (NaCl) crystals are dissolved in a beaker of clean water to form equal numbers of mobile Na+ and Cl" ions. The beaker is moved horizontally to the right with constant velocity vi: through a strong, uniform magnetic ﬁeld ~32 . The | t 73\$} electric ﬁeldE in the beaker is: *- a w B) E points in 2 direction with magmtude that depends on the density of ions C) E points in —2 direction with magnitude that depends on the density 3f ions {5 E) E=0 , the effect of equal + and - ions cancel out ‘ V 5,3. “g r 4 u it: I, I. will b]; «aw-ﬁn ﬁt” Z“ '5»- ‘ M r .m p v a f f {ENG-ﬂ {Add \2 1‘, + w," ’i‘ r" \C; {if}: swan} Jig“; i la tr" 2 e ‘ i“ 1‘, “ﬂ ari‘ﬁaﬁe" J ri { {Ajﬁ ax ggxgmgﬁ? it“ ' t 3 “W I if V l i ,5 r is: Q w; _;; w; an a a ﬂ» Version 1 Page 5 14. Four closed surfaces are shown. The areas Amp and Abe; of the top and bottom faces and the magnitudes BM, and Bbot of the uniform magnetic ﬁelds through the top and bottom faces are given. The ﬁelds are perpendicular to I - . :-= - - and are either inward or outward. Rank the surfaces according to at f the magnetic ﬂux through the curvedsides, least to greatest. ’ W an- 2em‘ B_.- 2 mT. inward 1 A“. .:c|11' . 2 m1: outwatd A,"- 2crn‘ Bull 2 mt Inward 2 X Al" 320'"! H Bmzﬁ ru'l'. outward A"! 2 I2I'I'lI B"- 3 mT. Inward 3 D a... 2cm‘ 5'... 3 mT.lnward O A“... 2 em‘ A“. 2 cm‘ BM:- 3 mT. outward 3m- 2 rnTI outward A) 1,2,3,4 B) l,2,4,3 C) 4,3,2,1 6370 3,4,1,2 ) 2,1,4,3 15. A I a -_l - late air-ﬁlled capacitor is charged with a battery to Q0 and then the battery is A dielectric with K=2.5 is inserted to ﬁll the plate spacing for half the area 0 e capacitor as shown. How much free charge is stored on the right half of the capacitor (the half where the dielectric is ? “*3; 3333’R M 0”;th 5 j 3 alpaca” N " t 5550a as, “500/620 M 6‘” a E) 0.42 Q0 2 .‘5 K Version 1 :[email protected]=o,7tag-—— Mgttgez Page 6 Q 16. An ideal 8 V battery is connected in series with a 5.0 Q. resistor and a second resistor of variable resistance R. By varying only the value of R, what is the maximum rate of energy dissi ated as heat in (and only in) resistor R that you can achieve? 8V R 2’46 K: —~ 8% ) WW {@531 8* 53\$ ,2 M t f ‘ H l 31"? ED; gisww lumen b"ﬁW\ _ 2Q “:17 "“ lg was» \L/ I a: (realm: 3,22. w 17. What must the resistor R be if the current through the 40 V battery is 1.5 A directed up? Version l Page 7 18. One type of spectrometer is shown in the ﬁgure. Particles of mass m and charge q are accelerated from rest through a constant potential difference V and then enter a uniform magnetic ﬁeld pointing straight out of the page. Which statement is true? V o a a IRI K6; z ‘ ' 1"“ 1' Dill-L' . R Jill? Barﬂy WWR Particles with low m and high q will have small R; Particles with the same product of m times q will have the same R.“ m) [1% C) Particles with the same q will have the same R irrespective of m. K) D) For equal charge particles those with higher In will leave the electric ﬁeld with lower velocity and hence have smaller R. E) For equal mass particles those with higher q will leave the electric ﬁeld with higher velocity and hence have larger R. Version 1 Page 8 19. A metal strip has current ﬂowing through its cross section that is 1.5 cm wide and 0.20 cm thick as shown. A uniform magnetic ﬁeld of 1.5 T is perpendicular to the wider, ﬂat face of the strip. The voltmeter measuring potential difference between the left and right (shaded) side-faces is 5.3 uV 01:10"). The drift velocity of the electrons in the strip in is approximately: A713 “gal/539i» 9015 A}; ‘55 .. 3r.‘e’e:m @535 03 :5} mmjw r H M. L l - ‘2. but) w»: A) 3.5 x IO'Zm/S ml 02513 3.5x 10:: m/s - p 95 1‘ \$2 2.4x10 m/s M is (:3 "3g 7.8x10'4m/s Q ’é’rinEE (3,. E) 20. On closing switch S the current throu . long time with the switch closed it is opened. a IS t 6 current through the 40 Q resistor immediately after this opening of the switch? 40 Q s ‘ TL: @WMOgeVﬁ/Q 9% gm) 2.00A \ jig/m lib-“ﬂ” “o B 4-00 A t 1.33A t) 3 “l 6,. ‘ __H [barf H ) 267A “TI to w-EM’” E) 0.75A it) Wants” Version 1 Page 9 ...
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