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Unformatted text preview: Student Name:  Student number: ___ Multiple Choice Questions (3 points each)
Clearly circle the letter of your choice; you do not need to show your work. No points will
be given to questions with two or more choices marked. No partial credit will be given. 1. A pingpong ball has a weight of5.0 x UTE N and is covered with a charge of 4.0 pC. What
electric ﬁeld directed ward will balance the weight of the ball?
a. 8.2 we2 we 6.2 x 10“ NC 0. 2.0 x 10‘7 NC d. 5.1 x 10" we 2. Which of the following best characterizes electrical conductors?
at are always uniformly charged bfpotential varies on the surface
@electric charges move freely daexpert on electric musical instruments 3. The beam of electrons that hits the screen ol'a TV is moved up and down by:
a: moving the electron source. b. a phosphorescent coating.
2: varying the electron’s charge. ®electric field between parallel plates. 4. Object A exerts an electric force, F, on object B. Object B has charge q, and object C has
charge —2q. Object A will exert what force on object C? Assume the same separation
distance in each case. a. F, opposite direction as for object B b. 2F, same direction as for object B
c. F, same direction as for object B @ZF, opposite direction as for object B 5. The plates of a parallelplate capacitor are pulled a small distance further apart. How does its capacitance change?
a. increase .decrease 0. remains the same d. None 0fthe above 6. Ifthe distance between two isolated parallel plates that are oppositely charged is doubled, the
electric field between the plates is essentially unchanged However, the
@ potential difference between the plates will double.
b. charge on each plate will double.
c. force on a charged particle halfway between the plates will reduce by half.
d. force on a charged particle halfway between the plates will become four times smaller. 7". Consider two charged spheres, one with charge +2 C and the other with —2 C. A proton is at
the point halfway between the spheres. What is n_0t zero?
a. the potential energy of the proton b. the work to move the proton from infinity to that point
@the force on the proton
. all of the three above are zero 8 If the voltage across a light bulb is doubled. what happens to the power dissipated? Ignore
the change in resistance due to a change in temperature.
a. It doubles.
.lt quadruples.
c. It increases by a factor ol‘2m.
d. It increases by a factor 01‘2”. 9. Two cylindrical resistors are made of the same material and have the same resistance. The
resistors, R. and R2, have different radii, ti and r2, and different lengths, L1 and L2. Which of
the following relative values for radii and lengths would result in equal resistances? In 2 [‘2 and L1: 2L2 b 21‘] = 1‘2 and L] = 2L;
13’. 1‘1 = [‘3 and 4L1: L2 @ZI'I = r2 and 4L 2 L2 ll]. The Eistiﬂty of a material is doubled when heated a certain amount. What happens to the
resistance of a resistor made of this material when heated the same amount? I doubles. b. It quadruples. c. It halves. cl. It stays the same. 9 .. 5 ,1; ..{u‘ Student Name: ; Student number: —_ Problems You must show all your work and use correct units for numerical answers to receive full
credit. Use the back side if needed. No credit for writing down equations only. 1 1. Two identical charges (q = —4.6 uC) are placed along a semicircle of radius 3.0 m, 30"
above the horizontal, as shown in the ﬁgure below (points A and B). (a) What is the resultant electric ﬁeld (magnitude and direction) at the origin of the .
coordinate system? (7 points) (b) if charge q] = —6 uC is placed at the origin, what is the electric force (magnitude and
direction) acting on this charge? (7 points) (c) Consider the two charges in (a), without q] at the origin. What charge (12 (magnitude and
sign) should be placed at point C so that the electric ﬁeld at the origin is zero? (7 points) Ezlﬂ
r
EA JSQ‘ixth m c (iéxlO‘SCi (3.0m)‘ 45949 Nlc would Acé
E3 = [mean mm; 4,991qu Q4 4594.? mic toward 8 (30 m)’ _L, _.o.
Crease” X4414 ‘0 CSIan’) (45‘34 ‘4 )
CO; 50 “X45140 CS‘mBo") (4594. ‘ll _._ ___ . .._.._.. __w—H—w ﬁrifﬁWﬁeﬁf) 4‘4 4 m .\
lEM’t = %§EWNIC_£fwa.rd _ Pain1 C“! / 6??) WWWH—mm.._¢_
.....,..___r F : 236 x {O'ZN— POEM 'U’) ‘HkQ OPPOSHQ direction OF truer
Pomi down H19. [1132 ,away {(007 POW C Hum—Mm 4444+] ‘ _ WC? 9M: 4 4 NOGomji "“1
_ Tifi‘ix[OCYNmi/C2 @9/ 12. Charge A (2.0 C) and charge B (2.0 C) are ﬁxed on the xaxis. Charge A is placed at x =
—~2.0 m and charge B at x = 2.0 m. (a) What is the electric potential mid point between them? (6 points)
(b) Find the electric potential at x = 3.0 m on the xaxis. (6 points)
(c) A third charge is moved to the origin of the coordinate system. What is its charge (sign
and magnitude) so that the electric potential at y = 2.0 m on the yaxis is zero? (6 points)
(d) What is the energy needed to move the third—charge from inﬁnity to the origin?
(7 points) ‘ a Vat;
VA :_ {9.94 x I07 NrnJ/c’ 2006) 2.0m A we 03 ' 3313c
VA: SFiGlXqu VoHS 63' ® ' VB = W : 239x :0" volt; 20 m .
Vrotal = VAtVB 7 QCSR‘inOl UoHS) 2‘ ’79? XﬂVoHS.
9 1 VA: MM MOC'N‘WC’ (30.9 = M?“ 10“ use '
e mam 5.0m 1 Va: (EH ‘lxtO‘1 — ’ c’ 2 : migx ,5me 5m thVAJrVB 3.5% X to“ + L795?! 0'0 watts 2.!576 X l0m .Hs.
.6)  (/~l\ __ T: ixzt—Y’ : ,1” 4— 11 : 2.82? m _ 2 ._\
aﬁg  . 7 if .t
A C 2 a VA  (W? X IO.N:m C )(206): 6.36 X ‘0? UDHJ. . 23:18 m.
VB = VA : (9'9. x (l .m’lc’ 2.0C’ : 6.36 Xqu VoHS
3‘929m' \/A r V; = 2 [6.36x 10"): (.272 xlo‘° VolLt
Vat" VB ‘l‘ VC :— 0
v“ Vs = —vc {KM} 59 A'PE= V% '[VAeﬂ r 2 {Cg/I'lﬂledowm) (30m
KG ((339 X IO‘lNm’kj APE M W a“) i
: 07?? X (0'0 VOHS) (“295 C) : PEA + PEB: 2 [ﬁg12052.0CJJ A =__,. ' 0 l0 ‘
PE 5 8331} x10 3’ C9
7/ 13. A 100 W light bulb is left on for 24 hours. (a) What is the electrica1 energy used up by the light bulb? (6 points) (b) in the US, the voltage in the power outlets is AV = 1 10V. Find the current that ﬂows
through the light bulb when connected to a power outlet. (6 points) (c) Find the resistance of the light bulb. (6 points) ((31) Find the charge that ﬂows through the bulb in 24 hours. (6 points) p:oow, i=24h' 3999i: 864003 lb
9 E 2 Pi: =Qoow)(8640083= S‘s 64xzo‘ J
b) szllov
p: IAV ___
I=_lo.mr_iQO_\/\l.__.__: 040? A /
A HO V :1 Z‘ ._______._....;—__ 2 J1
R 1‘ 0309A I) d  AG J 1'71? AG. : I Ail: ': (0907A).( 864008)/ Q2Z85X lOlLC ...
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 Spring '09
 Ganpathy

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