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Unformatted text preview: PHYSICS 1120 SECOND MIDTERM Name *DIO Student ID # You will lose 1 point on this exam if you do not correctly enter your Student ID number onto the
bubble sheet!!! Section number or Section Time:
Circle your TA’s name: MattAitken Maya F abrikant Nathan Hinkley Sunita Kannan Nathan Morrison John Papaioannou Ron Pepino Exam Version 0001 P1 11 t nth a ntil ar a k t . ' Your exam should have 11 pages, numbered E21 thru E2.11 ' This exam consists of 15 multiple choice questions, worth 5 points each, and a longanswer section
worth 25 points, for a total of 100 points. ' Write your answers in the space provided on each page for the written question. Use the back of
the page if needed. Circle the correct letter for the multiple choice questions. SHOW YOUR
WORK ON THE WRITTEN QUESTIONS. Full credit will be given only for the correct answer
accompanied by your reasoning. PLEASE!!
1. Print your name, your student Identiﬁcation Number on the page above.
2. Circle your TA’s name and write the time or Section number above.
3. Bubble your name, Student ID, and exam version number on the bubble sheet provided.
4. You do not need to bubble in the date or your gender. By handing in this exam, you agree to the following statement: "On my honor, as a University of
Colorado Student, I have neither given nor received unauthorized assistance on this work" Signature Possibly useful information:
k = 9.0x109 NmZ/Cz, e = 1.6x10‘19 C, so = 8.85x10'12 CZ/(Nmz)
mproton : 1.67X10_27 , meleczron : 9.11X10—31 Good luck! Spring 2010 132.1 Second Midterm Circle the closest answer and Bubble in questions 115 ON YOUR BUBBLE SHEET! 1. Two test charges are brought from r=oo into the vicinity of a charge +Qo. In the Situation 1:
ﬁrst situation, a charge of ~q is brought
to a point A, distance of r from the +Q0 _q
charge. In the second situation, a charge . .
of 2q is brought to Point B, a distance of r point A
2r from the charge. Which of the
following statements is true about the Sim t. 2'
potential (V) and the potential energy 3 Ion ‘
(U) of the test charges at points A and B +Q0 _2q
in these two situations. Assume that V=O . .
2r
at r=oo
v ' ' Point B
A V > V , U = U  .
CD) A B A B U * A395 DE" ‘ZKQﬁ
B)VA=VB,UA=UB k r. =UA
C) VA<VB,UA=UB 2r
D) VA = VB, UA > UB VA? —‘ \g‘ Q ch,
E) VA = VB, UA < UB I“ E 2) Two identical charges of +Q are ﬁxed in
space, as shown to the right. What is the
magnitude of the voltage and the magnitude _9
of the electric ﬁeld at the point that is ‘ =9
midway between them? Assume that V=0 at V '
r=oo,
° P
A) Both are zero _ _
Midpomt B) Both are nonzero A
C)::°f;‘:::::;§ am d, (m
_, 7 , 3mm we ﬂy)“ a.an ﬁWﬂtjﬁC E) Impossible to tell “a”. VstK n;
E as “Vealwﬁ 5?; k \I W at ttwwhﬁt”,?mm4(q\g Mt.de Spring 2010 E22 Second Midterm 3) The potential around an unknown charge
distribution is shown in the ﬁgure to the left.
Each equipotential contour is separated from the
neighboring lines by l 111. What is the
approximate magnitude of the electric ﬁeld at
Point P, which is halfway between the 4 V and 6
V equipotential lines? A) , 5‘le m ..
‘ N/C E g: "" “ﬁg? D) 4 N/C E)5N/C V
i% a”: m?» lW~
Aw 2M 4) The ﬁgure shows the equipotential
contours around three point charges, Q1,
Q2, Q3. Which of the following 005 statements are true? I. All 3 charges have the same sign. 0
II. The magnitude of the E—ﬁeld at point
A is smaller than at point B.
Ill. Q2 has a larger magnitude than Q1 _005
A) 11 only
B) 111 only _O'1 C) II and Ill  Q‘ afﬁx are nasil’m wigs,
A a; m Miriam” “‘ 9‘34 H greattvsi when Penman
\ms are, tweak *ﬁé’i‘wts‘, E; >E
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2.. Spring 2010 132.3 Second Midterm 5) Two parallel plate capacitors with the same plate area are shown below. The ﬁrst capacitor has a
dielectric with a dielectric constant of 4 between the plates. The second capacitor has no dielectric. If
the capacitance of Capacitor l is the same as capacitance of Capacitor 2, what is the distance between the plates, d2?
Capacitor 1 Capacitor 2 1d2=?? C 5 CL: 67A;
A) d2=d1 l d‘ 41
B) d2=2d1 \
C) d2=4d1 K K decr€otses b3 4', d2 \l/ b3 LI”
D)’ d2= cw dz; yﬁd‘ 6) Two parallel plate capacitors are charged isolation. Capacitor 1 (C1 =1 uF) initially has a net
charge of 2 ac on it. Capacitor 2 (C2 = 4 uF) initially has a net charge of 3 uC on it. Now you
connect the two capacitors to each other, with the + side of C1 attached to the + side of C2, and the —
side of C1 attached to the — side of C2. After they are connected together, how much charge ﬂows between the capacitors? Before: C1 C2 After: C1 C2
+01 +Q2 n
“(3‘ Q2 U
u‘m\ Charge, = Sac
MO'SHC Lane ’rtne are ca meted \/‘ We 5m
“ V‘ ‘1 V‘ C I ‘3 y
C) 2pc ow hm. Cass: CHCL {a u Cafaf‘hys
D) 311C Cob‘: Qw‘t :7 \[7 544C 2: fl, V
E) 4pc v maﬁa": s l as at
S a 2 s :H‘ é M on!
" 3.1.313 1M5 9.315: “E from cum (.2 7) In class you saw a pickle light up like a light bulb. It was plugged intoﬂthve 120 V outlet and was as
bright as 15 W lightbulb, so assume that the pickle consumed 15 W of power. What is the resistance of the pickle? 1 '2.
< A) 960 Q 5 """ M "’
B) 180 Q E’ K
C) 8 Q ,_..... a;
D) 0.125 Q E) 1.875 (2 Spring 2010 E2.4 Second Midterm 8) Apiece of copper is machined into the solid conical shape shown below. The ends of the piece of
copper are connected to a battery. Which region has the greatest current passing through it? A B C A) A B) B C) C ) Same in A, B, and C W Cuxré mi? 15 COWEZVWC‘. Tofa\ Cufwwx “macwwﬂh O“);
542:: (1,,we‘é’val \g Nd, WVWQ. Piv’idﬁa 9) Marty McFly is trapped in the year 1955. He needs 1.21 GigaWatts (1 GW = 109 W) to power his
time machine to take him back to the future. His friend Doc Brown has told him that only a bolt of lightning can provide this much power. If a lightning cloud at a height of 10,000 111 has an electric
potential difference of 107 Volts relative to the ground, how much current must ﬂow in the lightning bolt to operate the time machine? .W $9.3, iv “:3; f1; 1:» 1. Mathew
1% M" ' ' W ...
(1:2 12,.
B) 12:1 A
C) 121,000A ,_..
D) 1,210,000A “ I 3‘ A E) 121,000,000 A 10) Three resistors are shown below. Resistors 1 and 2 are made of the same material. Resistor 3 is made of a material with a resistivity that is 50% smaller than the resistivity of Resistors 1 and 2.
Resistor 2 has the same length as Resistor 2, but twice the radius. Resistor 3 has the same radius as Resistor 1, but twice the length. How do the resistances of these resistors compare? Resistor 1 Resistor 2 Resistor 3
A) R1 = 2R2 = R3/2 ﬂﬁgﬁaﬂ: 2L
Evil = 4R2 = 2R3
E) R1 = R2 = R3
as 9 VA
12. \ 2 "Egg Spring 2010 E25 Second Midterm The following two problems refer to the circuit below which has 3 identical light bulbs, each with
resistance R. The lightbulbs are connected to battery with a voltage of V. 11) What is the total combined resistance that the battery sees? =ﬁ+Yg=3~
A) 0.333R XL ‘ e a
B) 0.5R :E; ii ’3?
D) 9‘ E) 3R
W Eeeﬁarﬁ,
l 3‘3/22 12) How does the power dissipated in each bulb compare? ‘ A) P1 > PS?» B) P1 > P2> P3 C) P1 = P2: P3 D) P1< P2: P3 E) none ofthe above
w ﬁg ,1: 2. R 3;; haw ﬁﬁml (wwwtfs‘wm (goal AV
Comet" l > CwW’YZ': (wvei’itg > .5324: F? 13) Consider the mutli—loop circuit
at the right. Given the current
directions indicated in the ﬁgure,
which of the following expressions
is correct for Loop 1? A) V1 +12R1 +11R3 = 0
B) V1 12R1 11R3 =0
C) V]  12R1+ 11R3= 0 (1?)???le TEEQE
w... ....... WWW«4M E) V] +12R1  I3R3 = 0 “1:2 {ﬂaws OPt’T’OSKi'ﬂ lac>79} SQ K06» ,. (0mg (NW 4“ bop across gs? g" AV“: "" onh Midterm «new Q5 The next two problems refer to the two circuits shown below. Here lightbulbs are represented by 20 Q
resistors. In both cases the capacitors are initially charged to a voltage of 10 V. At time t=0, both
switches are closed, allowing the circuits to discharge. switch Switch
I
C=01 F R1 C=0.1 F R2; R3
(V0210 V) VO=10V
(20 S2) ( ) (20 g) (20 9)
Circuit #1 Circuit #2 14) After time t=1 second, what is the current through the closed switch in Circuit #1? A) lAmp 1— V git/KC
B) 0.824Amps ""2
C) 0.5 Am s ‘
0.303Am's , a; 10V "’ .1 FT
E) 0.184Amps  C y” i
101?; 15) Immediately after time t==0, which lightbulb is the brightest? All bullets See, the.
3313 ~ ' 94W AV at was
D)“ Clio, All E) R2 = R3», and both are brighter than R1
saw 1. 1? . V1 “s mums... “‘K UH“; iflagﬁ Spring 2010 132.7 Second Midterm E 135T Long Answer Problem: (15 points) Two charged parallel plates are shown below. The charge density on the plate on the right is —o, and +0
on the plate on the left. Assume that the plate size is very large compared to the separation between
the plates so that the plates can be approximated by inﬁnite charge? sheets. You will receive no credit for parts C—F without an explanation. +6 _6
d ,
(——————)
A B
0 O
C _ “*5 WW3?
En. X f”? A) Using the superposition principle for electric ﬁelds, what is the magnitude of the electric ﬁeld at
point B, which is halfway between the plates? Your answer may only contain 0, 7:, so and d. (2 points) F“; mm 4/ ﬂake E: __g_— ww‘sa, min?!»
M {awkw w "i‘ m: a. t“ km We 1r"? W W 3 m ‘xqgffhr * t “W m3, Q v A. A I
\p B) Draw an arrow below to indicate the direction of the electric ﬁeld point at point B? (1 point) C) Consider a negativelycharged test particle that is moved from point A to point B. Is AVA>B = VB
— VA, the electrical potential difference between point A and B, positive, negative or zero? (3 points) C' 1 . 't' ti " irc 6 one posz we .3 zero g) Eggnéour answer: AV : n if E ~t 69 AC are w“
.5. ‘ Same. dh'YCJﬁM . so ﬁ—ra AV <10 E" OTZX V 35 We mar Wear 4’ Chaﬁeﬁ,‘ 5.?
“Mod “4... “Mr Kg waWM am tower 1"“
Spring 20 l 0 E2.8 Second Midterm D) If the charge on the test particle were increased by a factor of 3, would the potential difference
AVA—>13 = VB  VA increase, decrease, or remain the same? (3 0‘ MMWN
Circle one: increase decrease remain the seiner“ Explain your answer: t,_ WW“ —> 5i .i \s ‘(mcegwfﬂf 9%
Arm eta w. 0% Arm +e‘s \r {Maﬁa . 13 NJ
25MB C€€Wiﬁd§ {3% sw‘mwoﬂgaj
charges . E) When our negatively—charged test particle is moved from point A to point B, is the change in
potential energy A   = UA, positive, negative or zero? (3 points) , , .
Circle one: negative zero Explain your answer: k’ﬁMﬁ {attﬁﬂik AM? Mg“ m ' £3,236.1pr
c\am~ m amt” , P F) Suppose that the negatively—charged test particle is now moved from point B to point C (which is
at the same distance from the plates as point B). Is AVB>C = Vc  VB , the electrical potential
difference between point B and C, positive, negative or zero? (3 points) Circle one: positive negative Explain your answer: V , . .
“aw «A: M :5 Cd)
\ *9 p m V
E is; Q i E '&mﬁs “€33; 5‘3 0 Spring 2010 E29 Second Midterm SE! :5 LN 12 Long Answer Problem: (10 points) In this problem assume that all of the lightbulbs HAVE THE SAME RESISTANCE, and all of the
batteries ARE IDEAL. You will receive no credit for an answer if you do not give an explanation. A) Consider the two bulbs connected to a
battery in parallel shown at the right. Initially the switch is closed. After the switch
is opened, what happens to the brightness of
Bulb A ? (4 points) The brightness of Bulb A (Circle one) increases decreases, but remains on ( stays the sang) goes to 0 Explain your answer: team we) a. at AV é _ , ‘
5‘s} 5Q“ 2‘2?wa 4;: that A t B) Now consider the circuit shown on the right.
Initially the switch. is open. Rank the brightness of Bulbs A, B, and C. (3 points) Your Ranking: . a» Explain your reasoning: l” 2;; if“? m‘ i ‘ Yr";
% up at.“ «up a g."sz Poi’c’yg ’n’q \ g i. m as \I WV a ? ~ 62"“
. H ' M
E Spring 2010 E210 Second Midterm C) Now the switch is closed in the circuit that was considered in part B. What happens to the brightness of Bulb C? (3 points) The brightness of Bulb C .... .. Circle one: increases decreases, but remains on stays the same goes to 0 wwin i
Explain: a cg i» ﬂwa
63¢ AYE sane ﬂaw? at“? mng A {qu saw a? tame W” mama2.. am£ w‘\\\ 3‘9 "Wﬂw J m»; m ﬁwlm’ @5ng”? we at, we Spring 2010 132.1 1 Second Midterm ...
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 Spring '09
 Holland
 Physics, Electric Potential, Electric charge, parallel plate capacitors

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