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Unformatted text preview: Exam 2 Foam j;
' ":74 1. A parallelplate capacitor is charged with a battery that is then disconnected. If the plate
separation of this charged capacitor is doubled:
7 A) the surface charge density on each plate is doubled
g B) the electric ﬁeld is doubled E  g
/e C) the potential difference is halved —
D) the capacitance is doubled E) @1173 offhe above ) Dwain 6,16% ‘0 2. A battery has an emf of 9V and an internal resistance of 29. If the terminal potential
difference is greater than 9V: A) it must be connected across a small external resistance 5"gg'g“) { ...— I} B) the current must be zero t d
’3) C) it must be connected across a large external resistance \
i D) the currentmust be out of the positive terminal _. "buca...“ Ef'fhe current must be 01f t“of'tﬁe"'negative1erﬁii'_hm?<=__ﬂj 3. The current density is the same in two wires. Wire A has twice the free electron
concentration (density) of wire B. The drift speed of electrons in A is: A) the e as that_g_f electrons in B ' _, ’9' B)@alf that of electrons in E ) J a; U0.
'3' C) twice at o 6 cc on m D) four times that of electrons in B
E) onefourth that of electrons in B 4. A hexagonal loop of wire carrying a counter clockwise current of 2.0 A has 6 sides that
are all 0.5 m long. A 0.7 T uniform magnetic ﬁeld is parallel to the base. The net
magnetic force on the 5 dashed sides has a magnitude of: A) 0.3ON / f 3* 2)
B) 0.51 N NE; _ a. C) 0.41 N p F” D N Fa? Egaiﬁi’ff‘ O ,x
G) 0 f“  f as ....*"' . wu _‘_ ﬁ .1‘ ‘t d Page 1 at?» 7/7» 5. A triangular solid in the shape of a 10 m wide inclined plane has height 3 In, length 4m
and ramp length 5 In. A uniform, horizontal magnetic ﬁeld B = 0.05 T is parallel to the
4m length. What is the magnetic ﬂux through the ramp face, shaded in the ﬁgure? (use
standard convention for normal vector direction of a closed surface) 6. A parallelplate capacitor, with air dielectric, is charged by a battery, after which the
battery is disconnected. A slab of glass dielectric is then slowly inserted between the plates. As it is being inserted: A) the glass makes the plates repel each other Wﬂassnut r
< C) a force attracts the glass into the ca acitor D) no force acts on the glass
E) a net charge appears on the glass (9?.
“a” 37:; “x
71665,” ﬁg 94>C5 Page 2 , '  s it
7. An electron and a proton each travel with e/gual speeds aiound circular orbits in the
same uniform magnetic ﬁeld, as shown in diagram (not to, scale). The ﬁeld is into
the page in the diagram. Because the electron is less massive than the proton and
because the electron is negatively charged and the proton is positively charged, which statement is TRUE: (B into page) i e’ F £0 13
O .3» P A) the electron travels counterclockwise around the smaller circle and the proton travels
clockwise around the larger circle B) the electron travels clockwise around the larger circle and the proton travels
counterclockwise around the smaller circle C) the electron travels counterclockwise around the larger circle and the proton travels
clockwise around the smaller circle D) the electron travels ecunterclockwise around the smaller circle and the proton travels
counterclockwise around the larger circle _ _ _ _ . 1 E) the electron"ti‘avels "clockwise aronnd't‘he smaller circle and the proton travels
counterclockwise around the larger circle. J . . __,_,_....._....‘—...‘—.u...._.......__‘_.........——.—‘ __._..   run—qua...“ ..........__———
_..__._._......_..— 8. Which of the following graphs best represents the currentvoltage relationship of a
typical ?5 Watt incandescent light bulb in a reading lamp? . ' . xx“ ‘ I
I I I
I . ‘ It . F
I : '4 Distwow)“ .. :ngw
V j; F V 31:? {1,333 C .
_ 3.125300%  Bewith winwages «J 101M ° I II I”
Ly b V
A) IV [T V 3 IV \ may. {WWM *TDTWLL?’
D) v 
E) II Page 3 12. The diagram shows a straight wire carrying a ﬂow of electrons into the page. The wire
is between the poles of a permanent magnet. The direction of the magnetic force exerted
on the wire, and any electric potential difference between the top of the wire and the
bottom of the wire are; Jim ..
N O S f
l I Fem OW“ A m < Vbot 3': C) ! vtop = ' bot a? < D) L , Vmp > Vbot E) T ’ Vtop > Vbot l3. Capacitor C1 is connected separately to a battery and charged until the magnitude of the
charge on each plate is qo. Then it is removed from the battery and connected to two
uncharged capacitors C2 and C3 as shown. The magnitude of the ﬁnal charges on the
capacitors are related by: 90=Q2+Q3,Q1=92 D) qu = Q) + Q3, q1 = 0' ' x‘a‘xx E) 90 = 971+ 632 + 633 14. A square loop of wire carrying 0.5A has a side length of 0.1m. The magetic dipole
moment initially makes an angle of 90° with a 0.5T magnetic ﬁeld. As it turns to 0 ' ned with the ﬁeld, the work done by the magnetic ﬁeld is: (
A 2.5 x 10‘ J I ~ 
_ — V .134.ch E “d: and 9M
B) 2. x J _ —3 , _
s a... I. Myjpstmmrm
E) 1.0x10‘ J . 2.11.: with!» 103 raw/@ng) 0 3
PageS : C. T 57% 425% 872. @4570 15. A certain ammeter has an internal resistance of 1 Q and a range from 0 to 50 mA (1 m
= 10'3A). To change its range to 0 to 5 A, i.e. make its full scale reading be 5.0 A, we need to add: 5/? f g a i A) a resistance of 99 Q in parallel
.__) . 05/} B) a series resistance of 99 D
D) anextr I.  lare 53 169) series resistance‘aLS'm‘DSJA @4401 L
E $ 3 I
) a re31stance of U99 (2 n1 arall __ . 05 _ Sl— C) a resistance of 111000 9 in parallel
16. An initially uncharged capacitor C is connected in series with a resistor R and a battery
of emf V0. Sufﬁcient time elapses so that a steady state is reached. Which of the folio ' is TRUE? " i 51!! '9?
AWme mm I g? 3
B) The time constant depends on V0 W W 6, W C) The total energy dissipated by R is independent of V0 (fare
D) The initial current (just after the battery was connected) depends on C _ C 91d,
Oil/Vila I l E) The ﬁnal charge on C depends on R
Mix/«WM a 17. A proton is in a region where a uniform electric ﬁeld of 5 x 104 Vim is perpendicular to
a uniform magnetic ﬁeld of 0.8 T. If its acceleration is zero then its speed must be: % wwjm m .
C)1.x s anvueu — E13 /
sow we as» 0% )3 18. Two Ohmic resistors R1 and R2 dissipate 25 W and 100 W respectively when
connected in parallel to a 100 V EMF. If instead we connect them in series to the same
EMF then the power dissipation rates are for R1 and R2:  soon A) SOWabd 12.5w 7’— _.
B) 12.5Wand50W J99: 25W R"
R: C 4Wand16W
2 —
was re.. m. ‘ semis I?» i
M Mai? :— w) Ezra—mu l9. Capacitors with capacitances of C and 2C are initially uncharged and connected to each
other through a resistor,R and open switch. The smaller capacitor is separately charged
with Q and the switch is then closed. What is the time constant for the charge
redistributionlsharing and how much energy has been dissipated as heat in the resistor once the potential difference across the capacitors becomes the same? meggﬂe El “35— ‘24”
l 1"” ya RC A) (213mg '(112) 21C .
B) 3Rc, (wag/C C) 2RC, (4!9)Q2§C CezDI—ﬂ’sc
D) R 1! I ‘2. ' a! 1... — l 7“ a m at g 3% Hf... 20. In a certain mass spectrograph, an ion beam passes through a velocity ﬁlter consisting of
mutually perpendiCular ﬁelds E and B. The beam then enters a region of another
magnetic ﬁeld B‘ perpendicular to the beam. The radius of Curvature of the resulting ion roportional to: C) 5333' 117 ....I $01 ’
 rs ) WM
53 3:12? 3 5 Page 7 9. A Specially prepared semiconductor has a free electron density of 1 x 1027 electronsfnf’
and free holes (a mobile entity with charge = +e) with density of 5 x 1027 holesfm3. In
an electtic ﬁeld of l x 104 Wm the electrons have drift speed of 3 x 10"4 Infs and the + ‘7 holes have drift speed of l x 10“4 mils. The resistivity of this material (in (2111) is
7‘1‘ 1’ about: . . .. E . "Emwﬂam
A) 0.05 ’ :. + I ' ‘7'  . I.
B) 0.0. J” J‘ J""’" S J 6(ntgo‘rﬂaﬁn)
C) 08 H
D) 0.11 :3. J0 E) 0.03 (Haggai [6&131’0 +‘15rJii7a‘lD J
:::§ 0.079.0_m 10. A portion of a circuit is shown, with the values of the currents given for some branches.
What is the direction and value of the cun‘ent i? A) l, 4A
B) l, 2A
C) T, 4A
D) T 6A
B) l,6A 11. A certain capacitor has a capacitance of 6 pF. After it is charged to 5 ,uC and isolated
(the charging battery removed), the plates are then pulled apart so its capacitance
becomes 2 11F. The work done by the pulling agent is about: 0 43
/ A) 4x10 J ﬂ vI, __
x1 I " I D)  2.. ,l a
E)12x10$l I»! L ,.... 5 am a. L“
_ 2... r” .
3.: l/ _ 1 2p}; (3)1}? ...
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 Spring '08
 DaveWinn

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