Physics C: Electricity and Magnetism
PHYSICSC
Section
I, ELECTRICITYANDMAGNETISM
Tlme-45 minutes
35 Questions
Directions: Eachof the questionsor incompletestatementsbelow is followed by frve suggestedanswersot
completions.Selectthe onethat is bestin eachcaseandthen fill in the correspondingoval on the answersheet.
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36. Thrce * uF caDacitorsarc connec0ed
in seriesas
L '
shownin thediagrarnabove.Thecapacitance
of
thecombination
is
.q3
38. A point charge+p is insidean uncharged
conductingsphericalshell that in tum is near
severalisolatedpoint charges,as shownabove.
The electric field at point P insidethe shell
dependson the magnitudeoI
(A)
' ' :uF
z '
(B) I pF
)
(C)
+uF
J '
(A)
(B)
(C)
@)
@)
(D)
' ' +uF
z'
I
(E)
' - +uF
o '
37. A hairdryeris ratedas1200W, 120V. Its
effectiveintemalresistance
is
(A)
0.1 o
(B) l0 o
(c) 12o
(D) 120o
(E) 1440O
O only
the chargedistributionon the sphereonly
Q and the chargedistributionon the sphere
all of the point charges
all of the point chargesandthe charge
distribution on the sphere
39, In a certainregion,the electricfield along the
r-axis is given by
E=ax+b.wherea=4OYhrP
andD=4Vlm.
The potentialdiffeiencebetweenthe origin and
. r = 0 . 5 mi s
(A) -36 V
(B) -7 v
(c) -3 v
(D) 10V
(E) 16V
734
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Physics C: Electricity and Magnetism
charged
42. A2O pF parallel-platecapacitoris fully
to 30 V. The energystoredin the capacitoris
mostnearlY
Questions40'41
X
X
X
X
(A) 9x103J
(B) 9x10-3J
(C) 6x 10-4J
(D)2x10-4J
(E) 2x 10-7J
X
AB
X
X
X
X
X
with
A Darticleof charge+e andmass ln moves
B
field
r*"i*r"
o"""taictilar to a uniform magnetic
a
is
alr""t"a ioto itt" page.The pathof the particle
circle of radius r' asshownabove'
the
40. Which of the following correctly gives
relating
equation
the
and
direction of motion
o and r?
Equation
Direction
(A) Clockwise
(B) Clockwise
(C) Counterclockwise
(D) Counterclockwise
(E) Couirterclockwise
eBr = mtt
eBr = ttw2
eBr = mu
eBr = mtt2
eBr2 -- mtt2
41. The period of revolutionof the particle
(A) mr
"B
(B) 'll^
eE
2nm
(c) -E
,-E
eB
is
43.
'-' A ootentialdifference V is maintainedbetween
i*i1**". p*ullel conductingplates'An electron
.tu.t. fon te.t on the surfaceof oneplate and
acceieratestowardthe other' Its speedas it
reachesthe secondplateis propodionalto
(A) ltv
(B) ruJV
(c)
(D) v
(E) v2
44. A wire of radius R hasa current I uniformly
distributedacrossits cross-sectionalarea'
l*p"tt;. tu* it usedwith a concenniccircular
radiusr, with r < R, to calculatethe
oath'of
'maenitude
of the magneticfield B at a distance
froir the centerof the wite' Which of the
following equationsresultsfrom a correct
6r n perc's law to this situation?
"ppril"ai"
(A) B(2xr) = PoI
@) B(zxr)=
",(*)
Q) BQnr) = o
(D) BQrR) = PoI
=
@)B(ztuR)
",(#)
(D) '"1
-@(E) .-'"rtl
eB
iflcoprylng or tcu.c ol
ol thl. prgp l. lll€gd'
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135
Physics C: Electricity and Magnetism
Questions45-46
Q
W
-
4
Q
Particlesof charge Q and-4p arelocatedon
the -r-axisasshownin the figure above.Assume
the particlesareisolatedftom all othercharges.
45. Which of the following describesthe directionof
the electric field at point P ?
(A) +r
(B) +v
(c) -v
(D) Componentsin both the -r- and +y-directions
(E) Componentsin both the +t- and-y-directions
46. At which of the labeledpoints on the r-axis is the
electricfield zero?
47. When the switch ,Sis openin the circuit shown
above,the readingon the ammeterA is 2,0 A.
When the switch is closed,the readingon the
ammeterrs
(A)
(B)
(C)
(D)
G)
doubled
increasedslightly but not doubled
the same
decreasedslightly but not halved
halved
48. Two conductingcylindrical wires aremadeout
of the samematerial.Wire X hastwice the length
and twice the diameterof wire L What is the
p
(A) A
(B) B
ratio =l
K..
(c) c
of their resistances?
(A)
+
(B)
+
(D) D
(E) E
(c) I
(D) 2
(E) 4
136
rlz6d copylng or llut€
ot llrlr Dllc lr lll.od.
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Physics C: Electricity and Magnetism
I
I
I
I
I
surface'A graphof-electric
49.
- A solid metallic sphereof radius ft hascharge Q uiformly distributedon its outer
the
V as a function of poritioo r is sho'wnabove.Which of the following graphsbestrepresents
*tentiaf
-magrritude
of the electricfield E asa function of position r for this sphere?
(B)
(A)
(D)
I
-----{
ot lhl.
I
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737
Physics C: Electricity and Magnetism
50, Two parallel wires, eachcarrying a cunent 1,
repeleachother with a force F. If both currents
aredoubled,the force of repulsionis
(A) 2F
(B) 2JTF
(c) 4F
@) 4JZF
(E) 8r
51. A circular current-carryingloop lies so that the
planeof the loop is perpendicularto a constant
magneticfield of strengthB. Supposethat the
radius R of the loop could be madeto increase
with time t so that R = dt, where a is a constant.
What is the magnitudeof the emf that would be
generatedaroundthe loop asa function of I ?
(A) 2nBazt
(B't 2nBat
(C) 2nBt
(D') xBa2t
(E) f;n"2f
'ol-_l-
'^i-l_
€=i
r=
+
lov
'l__l_ , +
f_l-_
20v
I
52. The figuresaboveshowpartsof two circuits, each
containinga batteryof emf € and intemal
resistancer. The currentin eachbatteryis I A,
but the directionof the currentin onebatteryis
oppositeto that in the other.If the potential
differencesacrossthe batteries'terminalsare
10V and20 V as shown,what arethe valuesof
t andr?
(A) € =5V,r=15 O
( B ) €= 1 0 V , r = 1 0O
( C ) €= 1 5 V , r = 5 Q
(D) € =20v,r=10 Q
@) The valuescannotbe computedunlessthe
completecircuits are shown.
53. A chargedparticle canmove with constant
velocity througha region containingboth an
electricfield and a magneticfleld only if the
(A) elecaic field is parallel to the magneticfield
@) electricfield is perpendicularto the magnetic
field
(C) electricfreld is parallel to the velocity vector
(D) rnagneticfield is parallelto the velocity vector
@) magaeticlield is perpendicularto the velocity
vector
138
ot thlr
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Physics C: Electricity and Magnetism
oirilnr.oop
is Pulled
54. A conductingloop of wire that is initially around
a magnetis pulled awayfrom tlte magnetto the
right, asindicatedin the figure above,inducing a
currentin the loop. What is the direction of the
force on the magnetandthe direction of the
magneticfield at the centerof the loop dueto the
inducedcurrent?
Direction of
Forceon the Magnet
(A)
@)
(C)
(D)
(E)
To the right
To the right
To the left
To the left
No direction;
the force is zero.
ot lhir
Direction of
MagneticField at
Centerof Loop due
to InducedCunent
To the right
To the left
To the right
To the left
To the left
55. A squareloop of wire carrying a current 1 is
initially in the planeof the pageandis locatedin
a uniform magneticfield B that pointstoward the
bottom of the page,asshownabove.Which of the
following showsthe correctinitial rotationof the
loop due to the force exertedon it by the magnetic
field?
(A)
(B)
(c)
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139
Physics C: Electricity and Magnetism
I
Rz=20 dl
57-5E
Quesdons
+Q
+9/
.?i
+9...
+a
i
i+Q
+Q
56. In thecircuitshownabove,theequivalent
resistance
of thetlu€€resistors
is
(A) 10.5()
(B) 15 ()
(c) 20cr
(D) 50 (,
(E) 115O
As shownin the ftgure above,six particles,each
with charge+p, areheld fixed andareequally spaced
aroundthe circumferenceof a circle ofradius R.
57. What is the magnitudeof the r€sultantelectric
field at the centerof tbe circle?
(A) 0
9=
@) r{o
+xeo Rl
Q +raeo
+ 4Rz
(D) iJ2
Q
4xes I8
(E)
3
Q
2xcs L2
5E.With the six particlesheld fixed, how much work
would be requiredto bring a seventhparticle of
cbnge + Q from very far awayandplaceit at the
centerof the circle?
(A) 0
(' B ) 6
o
4fteo R
G'+;
Q2
R2
,r*
Q,
R
@2-+
E€o
740
ol thl.
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Physics C: Electricity and Magnetism
Questions59-61
61. Howmuchnetworkmustbedoneby anextemal
forceto movea -1 pC pointchargefromrestat
poirt C to restat point E ?
(A) -20 uJ
(B) -10 rtJ
(C) l0 rrJ
(D) NN
(E) 30 pJ
62. Oneof Maxwell's equationscanbe written as
.
The diagramaboveshowsequipotentiallines
producedby an unknownchargedistribution.
A, B, C, D, and E arepoints in the plane.
59. Which vectorbelow bestdescribesthe direction
of the electricfield at point A ?
( ) , /
@)
,/
.1A
e. as = -:{3.
J0
d
t
fact that
Thisequationexpresses
the
(A) a changingmagneticfield producesan
electricfield
(B) a changingelectricfield producesa magnetic
fie1d
(C) the net magneticflux througha closed
surfacedependson the currentinside
(D) the net electricflux througha closedsurface
dependson the chargeinside
(E) electricchargeis conserved
(c) \
(D) \
@) Noneof the above;the field is zero.
60. At which point doesthe electric field havethe
greatestmagritude?
(A) A
(B) B
(c) c
(D) D
@)E
of tfil.
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4 /t4
Physics C: Electricity and Magnetism
qF
*d-l
63. The platesof a parallel-platecapacitorof crosssectionalareaA areseparatedby a distanced,
as shownabove.Betweenthe platesis a dielectric
materialof constantr(. The platesarecomected
in serieswith a variableresistanceR and a power
supplyof potentialdifference V. The capacitance
C of this capacitorwill increaseif which of the
following is decreased?
(A) A
(B) R
65. A physicsproblemstarts: "A solid spherehas
chargedistributeduniformly throughout. . ." It
may be conectly concludedthat the
(A) electric field is zeroeverywhereinside the
sohere
(B) electric field insidethe sphereis the sameas
the electricfield outside
(c) electricpotentialon the surfaceof the sphere
is not constant
(D) electric potentialin the centerof the sphere
is zero
(E) sphereis not madeof metal
Questions66-67relate to the circuit represented
below. The switch S, after being openfor a long
time, is thenclosed.
(c) ,<
(D\ d
(E) y
66. What is the currentin the cfucuitafter the switch
hasbeencloseda long time?
(A) 0A
(B) 1.2A
(c) 24,
(D) 3A
(E) 12A
64. The currentsin threeparallelwires, X, Y, and Z,
eachhavemagnitude1 andarein the directions
shownabove.Wire Y is closerto wire X than to
whe Z. T\e magneticforce on wire I is
(A)
(B)
(C)
(D)
(E)
zero
into the page
out ofthe page
towardthe bottomof the page
towardthe left
67.Whatis thepotentialdifferenceacrosstheresistor
immediately
aftertheswitchis closed?
(A) 0v
(B) 2v
(c) 7.2V
(D) 8v
(E) 12v
Unauthoalz€dcopvlhg or rru!6 ot
742
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Physics C: Electricity and Magnetism
68. A uniform sphericalchargedistributionhasradius
R. Which of the following is true of the electric
field strengthdueto this chargedistribution at a
distancer from the centerof the charee?
(A)
(B)
(C)
(D)
@)
x
B
x
Pr
x
It is greatestwhen r = 0.
It is $eatest when r = Rl2.
It is direcdy proportionalto r when r > R.
It is direcdy proportionalto r when r<R.
It is directlyproportionalto l.
X
X
P2
X
X
70. A sheetof copperin the planeof the pageis
connectedto a batteryas shownabove,causing
electronsto drift throughthe coppertowardthe
bottom of the page.The coppersheetis in a
magneticfield B directedinto the page.P1 and
P2 arepointsat the edgesof the strip. Which of
the following statementsis true?
69. When a negativelychargedrod is brought
near,but doesnot touch,$e initially uncharged
electroscopeshownabove,the leavesspring
apart(I). When the electroscopeis then touched
with a finger, the leavescollapse@). When next
the finger and finally the rod areremoved,the
leavesspringaparta secondtime (IIf. The charge
on the leavesis
(A)
(B)
(C)
(D)
@)
(A)
(B)
(C)
(D)
(E)
Pl is at a higherpotentialthan Pr.
P, is at a higherpotentialthan Pt.
P, and Pr arc at equalpositivepotential.
Pr and P2 areat equalnegativepotential.
Currentwill ceaseto flow in the coppersheet.
positive in both I andIII
negativein both I and trI
positive in I, negativein Itr
negativein I, positive in III
impossibleto determinein eitherI or III
ENDOF SECTIONI. ELECTRICITY
AND MAGNETISM
lhsllFrL.d
a rrof
coptlE d llrr
fta. m
blllal.
743
Chapter V: Answers to the
2004AP PhysicsC Exam
.
.
.
'
SectionI: Multiple Choice
. SectionI Answer Key and PercentAnswering
Correctly
. Analyzing Your Students'Performanceon the
Multiple-Choice Section
. Diagnostic Guide for the 2004 AP PhysicsC
ReleasedExam
MechanicsQuestion 3
Electricity and Magnetism Question 1
Electricity and Magnetism Question 2
Electricity and Magnetism Question 3
Section I: Multiple Choice
SectionII: FreeResponse
. Comments from the Chief Reader
. Scoring Guidelines,SampleStudent Responses,
and Commentary
. MechanicsQuestion I
. MechanicsQuestion 2
Listed below are the correct answersto the multiple-choice
questions,the percentofAP studentswho answeredeach
question correctly by AP grade,and the total percent
answeringcorrectly.
Section I Answer Key and Percent Answering Correctly
lMechanics
Item
No.
Correct
Answer
2
3
D
E
4
5
6
7
C
B
B
10
D
E
1'T
c
I
C
13
14
D
15
17
20
21
22
23
26
27
28
29
30
31
32
35
Percent Correct by Grade
5
4
3
2
r
96
93
64
92
75
70
95
3 7
79
89
a7
a2
97
88
80
97
6 8
93
76
7'I
68
62
66
63
91
84
2 7 7
64
47
B5
42
62
23
42
99
69
61
87
98
5'.7
46
75
98
57
42
64
96
47
36
52
45
32
2S
27
Correct
Answer
5
36
37
3B
E
B6
BO
a7
6B
BB
33
39
40
B
C
76
55
62
4A
41
C
66
3B
42
43
51
44
41
82
52
54
71
63
7
Item
No.
7
23
82
35
26
34
22
96
44
66
33
53
62
38
81
61
47
37
17
C
BB
75
60
42
27
E
D
B
E
E
58
75
57
78
39
34
27
52
27
36
27
12
18
77
46
10
2a
BB
70
B
C
90
85
40
9B
22
56
42
73
49
75
75
B
25
Electricitv and Maqnetism
Total
Percent
Correct
87
C
D
E
C
C
c
D
c
B
92
93
48
81
70
63
55
48
61
62
97
21
77
50
52
53
19
58
4a
30
63
B0
17
94
75
14
50
79
23
5B
34
33
5B
B9
31
24
39
63
26
50
30
'12
B
45
23
34
11
45
37
32
41
34
21
3L
23
18
17
17
19
6
30
6
26
26
'13
L2
B
C
B
B
C
C
C
B
60
43
62
6l
62
59
63
64
22
35
43
39
28
33
65
66
67
94
65
83
71
85
81
44
81
48
C
83
D
99
96
D
59
4A
a4
73
7B
83
63
B1
7'r
5i
37
61
41
30
33
50
54
55
56
57
'12
66
E
48
49
Pelcent Correct by Grade
4
3
2
7
B
B
63
61
28
53
82
43
65
47
37
26
43
35
25
'17
6
I
30
12
13
24
10
29
62
26
54
42
33
21
3B
22
23
4A
16
37
52
69
32
29
60
24
57
55
36
39
49
B
23
3B
30
49
73
17
24
4A
10
20
43
10
41
56
64
54
91
1a
20
72
47
16
36
'12
45
32
26
10
24
97
94
90
36
91
7A
6f
49
28
23
15
15
5B
33
27
25
53
80
36
43
42
37
54
71
65
46
35
25
i6
61
39
36
31
29
22
20
16
85
64
66
48
48
34
16
53
43
27
58
34
23
44
3B
25
14
5
71
55
59
40
49
27
36
64
15
4a
27
27
B
T7
B
32
D
82
E
E
77
C
42
50
65
49
49
Total
Percent
Correct
71
65
50
6B
BB
79
6B
D
73
69
D
44
33
37
30
70
B
28
I3
11
35
I5
L61