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Unformatted text preview: Physics 0175 — First Hour Examination
February 8, 2008 Page1 of 6 Print Your Name: ManeI’ ***IMPORTANT NOTICE*** Before you start the test, print your name on each page. Use the blank space provided after each question to work out the problem. WRITE NEATLY! No partial credit will be given if your writing is illegible. And no
credit will be given for a numerical answer that' Is correct but not accompanied by
any written equations that show us how you arrived at your result. Be sure to enter your final answer into the marked box whenever such a box Is provided Express numerical answers with the appropriate number of significant figures
and give units when appropriate. DO NOT WRITE IN THIS BOX!
Problem
Total Test
_ K a Problem #1 25 oints: (a) The electric ﬁeld lines for a fixed arrangement of charges never cross. But consider what
would happen if electric field lines did cross each other. What would it mean if two electric
field lines were to cross? Circle your choice. (5 points) (A) A test charge placed at the intersection of two electric field lines would be torn apart
and travel in two different directions. A test charge placed at the intersection of two electric field lines would experience a
force in two different directions. (C) A positive test charge placed at the intersection of two electric field lines would follow
one of the lines and a negative test charge would follow the other line. (D) The electric field at the intersection point would be infinitely large. (B) The electric field at the intersection point would be zero. Physics 0175 — First Hour Examination Page 2 of 6
February 8, 2008 Print Your Name: if! g gist: (b) The diagram below shows four point charges that are placed on the two perpendicular axes
equidistant from the crossing point. If a +Q point charge were placed at the crossing point,
into which quadrant would the net force point that the other four point charges exert on it?
Circle your choice. (5 points) (A) Quadrant 
(B) Quadrant ll @ Quadrant m (D) Quadrant IV
(E) None; the net force is zero. (c) The charge on an originally uncharged insulated conductor A is separated by induction from
a positively charged nonconducting rod B brought near the conductor without touching it
(see diagram below). The five closed dashed lines represent five closed Gaussian surfaces. For which of these Gaussian surfaces is @EdE = 0? Circle your choice. (5 points) (A) Surface S1
Surface 82
(C) Surface 83
(D) Surface 84
(E) Surface S5 (d) In the diagram below the dashed lines represent five parallel equipotential planes that are
perpendicular to the plane of the page. An electron moves from one equipotential surface to
another along five different paths that are shown by the solid lines. Which path will result in
the largest increase in the electron’s kinetic energy? Circle your choice. (5 points) @Patm w: +3oev “7% AKE >0/50
(B) Path2 w s + [0 eV i 3: i 3 'i 149+ work alone
(C) Paths w: +toet/ 5 4 = i ‘ 3 Oue'ds >0 (D) Path4 w= zaeV i 5 3 i .3 3 Es road, has”?
(E) Path5 w: ~‘loel/ ' . ' ... +90V +8£JV +70V +60V +50V 50 Fe O“ C'Pocufs (e) Two conducting spheres, with one having twice the diameter of the other, are/gecpérgted by
a distance that is large compared to their diameters. Initially the smaller sphere (1) has net
charge q and the larger sphere (2) is uncharged. If the spheres are then connected by a
long, thin wire, which of the following statements is true. Circle your choice. (5 points) (A) Each sphere ends up with charge (q/2) (D) Sphere 2 has half the potential of sphere 1 (B) All of the charge is dissipated in the wire @The spheres end up with equal potential
(C) Sphere 2 has twice the potential of sphere 1 Physics 0175 — First Hour Examination Page 3 of 6 February 8, 2008
Print Your Name: H ggﬁgr
Problem #2 (25 gointsl: The adjacent diagram shows five identical point charges of
charge Q=+15.0nC which are placed with uniform spacing
along a semicircular arc of radius R=0.250m. (a) Determine the magnitude of the electric ﬁeld that
any one of these point charges produces at the origin
of the x—y coordinate system. (5 points) .s Q 3
lEl= K E;=,Z.léxl0 ’V/c/ ~“1 Q My answer is: (b) Based on symmetry considerations, what is the direction of the total electric field that
all ﬁve point charges produce at the origin? You must describe your reasoning. (5 points) gmmu 5+ Pa L‘W+ L‘L‘ p0$. X‘Oh'l/CC'I'LUK Myansweris:
b/c we ywwpéa¢n+>a,ﬁ S cancel {or
GWV7¢$ la 5’ 0:444 0‘44,qu 2491.;905. X (0) Calculate the magnitude of the total electric field that all five point charges produce at
the origin. (10 points) (Ebt‘ 53X+ szl—qu = K%(l+coslls’+cas‘!$'>
. a a
= K €101 2am¥5>= ICEJ23”) s
= 52!“? ”A My answer is: (d) Determine the magnitude and the direction of the total electric force that these five point
charges would exert on a point charge q= ~650uC if it were placed at the origin. (5 points) .3 (”it ._5 = W'IEbt)‘ 3'3“,
alcvectCam CS uej. X.‘ 10/; $ (.5 W83. 4463. X W Eat L's cu pas. x—olz‘recl—cbq My answers are: Physics 0175 — First Hour Examination
February 8, 2008 Page 4 of 6 Print Your Name—ML—
Problem #3 (25 points): The adjacent diagram shows a cut through two
concentric spherical shells made of conducting
material. The inner and outer radii of the first shell
are a=O.100m and b=0.160m, respectively. The COWdUC'COr
corresponding radii for the outer shell are
c=0.240m and d=0.300m. The inner conducting
shell has a net charge q1=+25.0nC. The outer
conducting shell has zero net charge. An isolated
positive point charge q2=+1O.OnC is located at the
center of the spherical cavity inside the inner shell. (a) Determine the magnitude and direction of the
electric field at r=0.080m. (5 points) $45} W773 g'“ = Q; 59 So » l
————> rel: (55.23 %= [fwxloyN/O E Fotu‘l’s Yadt'alty out b/C g; C5 {795. (b) How much charge resides on the inner surface of the inner shell? You must give a
reason for your answer. (5 points) ¢= 0 {ov a Saussvaut surfacg euh'rely thllu'k the. i'uuer
She,“ We 5:0 CULSL‘de Hae, shell. #euce, $cu¢=ﬁlénsiznc¢ $1
L's Cu Hm cawo'tyl Hime, must'be, 41¢ch, 91L "fz=" (0.0 MC, :9“ H12 Comer Suvfac: "
0% HALL L'wwv ghell. (c) How much charge resides on the outer surface (r = b) of the inner spherical shell? You
must give a reason for your answer. (5 points) We L‘wuw slut,“ LULS «Kati dune ¥,=+ZS0KC. IF “l0.0\.\(‘, [3 out H’s t'waeu sow Facc,f'herc 144qu Myansweris:
be, q! + “long a+3$'.0uC, 0K n+5 austeu <cw face, + 35:0“ Physics 0175 — First Hour Examination
February 8, 2008 (d) Determine the total electric flux through a closed spherical surface of radius r= is concentric with the shells. (5 points) (75 __ ? eucl
r _____. go ”6"“ be+weem Hm HM $(IeI/5 MM ﬁzem e +350 “C + . L 3
o (e) Determine the magnitude and direction of the electric field in the region outside the outer gene! = shell, at a radius r=O. 320m. (5 points) <¢r ‘ ﬂ“ = Erttrtz>= M T E”! ___\__ ﬁend _ +350ML((
( Hrs.) .r" ‘ (0.320)?— titre; Eye 3.0? “031% dt'VQ¢+l:oUL of E4, s’; Tahiti/y on?”
Problem #4 (25 points): The adjacent diagram shows the region between two large, parallel conducting plates far from the edges so that edge effects can be ignored. The left plate is maintained at a constant electric potential VL=+80.0V and the right plate is
maintained at a constant electric potential VR=—40.OV. The y
gap between the plates is d=8.00cm. The dashed lines L
shown in the diagram represent three equipotential surfaces x which are located at equal intervals of d/4 between the
plates. (3) Calculate the values V1, V2, and V3 of the electric
potentials of the three equipotential surfaces. (6 points) AV: VR—VplZav
SCMC¢ erfucpolekffml Sthaus are spaced 0% apkrf 044A IE]: CQKS‘LQMJL H‘L)’ ‘rC
30V dq’or‘l’ lk pointHad . U: 5‘0. ml; {that geuol. 59 P05 sz 20.0V ~ V,=——Iam/ I Page 5 of 6 Print Your Name: H g S‘Itl/ 0.200m that My answer is: )‘(B HM; jaugc'aq jun—154cc L's: a'a Ht: +3$0~C Physics 0175 — First Hour Examination
February 8, 2008 Page 6 of 6 Print Your Name: M Q 512$! (b) Determine the magnitude and direction of the electric field that exists in the region
between the parallel plates. (4 points) Silence. g "S Cék$+au+ :1 AV _ l 20V My answers are:
t:="A;="( )=/5’00V/
magma Wt (wants in +X oli'rm‘zbq (0) Calculate the work done by the electric field on a point charge of q=+400uC when it
moves (i) from Point A to Point B and (ii) from Point B to Point C. (Points A and B have
the same xcoordinates and Points B and C have the same ycoordinates.) (10 points) (C) since A Md 3 are cu. Sawc cgm'fm‘ewlt’a/ Stir/4c: WA 5 = 0 My answers are: (ii) W50: ? E'A;5c=(‘{0”/‘C)(’5°” y") ‘
40.0w) (able? :  24.9 m: (d) Calculate the change in the electric potential energy of this same point charge when it
moves directly from Point A to Point C. (5 points) A MAC = g (VC—Vﬁzwwftcﬂeou): +2742 m :7 My answer is: AuA¢= 917.0 “Aj END OF TEST ...
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 Spring '08
 Koehler
 Physics

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