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Unformatted text preview: Physics 241
Fall 2008 Exam 1 October 1, 2008 Giving information to or receiving information from another person while taking this
exam is cheating. To intentionally do anything that would cauSe the level of your
knowledge of the material to be misrepresented is cheating. Anyone found to be cheating
will receive an F for the course and their names will be forwarded to the Dean of Students. Physics 241, Exam 1 Equation Sheet
N 2 ‘ 2
k=9109 C”: k=4l so =9.1(I‘2 NC 2 1eV= 1.610“"J 6:1610"?
71'8 m ¢=jE.ﬁdA hid/4:9 szvb—Vaz— Edi dU=—17‘df F=qE
S S 80 a dv—figu ~Edf v=£‘i V: 3‘1 Ex——d—V E “ﬂ Ez——§—‘:
qo r 1r“t ' dx y dy dz a I a! d 1 2 1 3:19: 1/:ij (3:9 C=80A VQ— U=—g—=—QV=iCV2
Ar r v of 3A 2C 2 2 2 9 O
J'cos(9)a’8:sin(6) Isin(9)d9=—cos(6) 3291 d—r=1n(r) jrd9=r9
r r r
2
r
d = d =—
J r I” I?“ F 2 Question 1 What is the magnitude of the electric ﬁeld at point P? 1 2Q2
(a) 47:80 7 1 Q_2 d
(b) 47:80 d2
(C) I JEQ ' _
47:80 62 r—T—F
I Q P W" 1 — 2
47580 d (d) (e)13
2 47:80 d Question 2 What is the electric potential difference at point P? a) 1 471780 d 1 9. (b) 427:80 d2
1 2_<22 (C) 47:60 0!
1 i
42:8G JEd
1 2
(e) Q 47:50 cl—2 (d) Question 3 In the diagram, which two points are closest to being at the same potential? (a) A and D
(b) B and C
(c) B and D
(d) A and C
(e) Potential is not deﬁned here Question 4 A large negative charge —Q is located in the vicinity of points A and B. Suppose a
positive charge +q is moved at constant speed from A to B by an external agent.
Along which of the paths shown in the ﬁgure will the work done by the ﬁeld be the
greatest? (a) path 1
(b) path 2
(c) path 3
(d) path 4
(6) work is the same aiong all four paths. Question 5
The electric charge on a conductor is (a) uniformly distributed throughout the volume. (b) conﬁned to the surface and is uniformly distributed. (c) mostly on the outer surface, but is not uniformly distributed. (d) entirely on the surface and is distributed according to the shape of the
object. . (e) dispersed throughout the volume of the object and distributed
according to the object’s shape. Question 6 In the ﬁgure, which best represents the ﬁeld lines due to two spheres with equal
and opposite charges? Question 7 Two identical conducting spheres, 1 and 2, carry equal amounts of charge and are
ﬁxed a distance apart that is large compared with their diameters (shown in part a).
The spheres repel each other with an electrical force of F. Suppose now that a
third identical sphere 3, having an insulating handle and initially uncharged, is
touched ﬁrst to sphere 1(shown in part b), then to sphere 2 (shown in part c), and
ﬁnally removed (shown in part (1). Find the force between spheres l and 2 now. (a); (nil: «2»ng @ng (e) same F Question 8 The nucleus of an iron atom has a radius of 4  10'15m and contains 26 protons.
What is the magnitude of the electrostatic force between two protons separated by one radius? (a) 1.410'6N
(b) 14 N (c) 5.210'4N
(d) 3.6102N
(e) 3.6105N Question 9 Use Gauss’s Law to ﬁnd the magnitude of the electric ﬁeld at a point B a distance
R from an inﬁnitely long straight Wire. The wire has a uniform charge density 1.
per unit length. P
(a) E: 1 AR2
27:80
1  R
(b) E: 2E8 AR '
(c) E: 1 mm)
47580
1 A
(d) E* 47580 R2
1 5L
(6) E— 21:8 l1" Question 10 Find the electric potential due to a rod of lengthﬂ at point P, with uniform charge
density 11 , as shown in the Figure. )1
471780 1 (b—a)/'L A
(b) 42:80 62 77 z x9
2 ———+—m x
(c) 1 33(9) ' “ﬂag. (a) 1n(b/a) 47:80 a
1 M
d
( ) 47:80 (b—a)
l M
(e) 47:80 (b ~— a)2 Question 11 A conducting shell carries a total charge of +4 LLC. A point charge A of +3 11C .is inside the shell; a point charge B of 2 [1C is outside the shell. What is the total
charge on the outer shell of the conductor? (a) +2 itC
(b) +1 tLC
(c) +5 [1C
((1) 5 itC
(e) +7 tLC Question 12
A plate carrying a uniform positive charge lies on the x—y plane away from the zaxis, as
shown in the Figure. Which of the following graphs describes the electric potential on the
zaxis? Note: The z—axis does not pass
through the charge distribution. Question 13 Each side of a metal plate has a surface area of 0.1 m2. The total charge on the
plate is +10 nC, or +5 nC on each surface. It is placed in a uniform electric ﬁeld
of 104 V/mgwith both surfaces perpendicular to the electric ﬁeld. What are the
ﬁnal charges on each surface? Q
(a) 9 nC +9 nC , l I
(b) —9 HC +l9nC E. i (c) —4 nC +14 nC w_____, m,
(d) —5 nC +9 nC (e) 3.5 nC +8.5 nC 1
————¥ ———>
plate Question 14 A ﬂat sheet of paper of area 0.25 m2 is oriented so that the plane of the sheet is at
an angle of 30° (as shown in the diagram) to a uniform electric ﬁeld of magnitude
14 N/C. What is the magnitude of the electric ﬂux through the sheet? (a) 3.0 Nm2/C
(b) 1.8 Nm2/C
(c) 0 Mr M
(d) 3.5 Nm2/C _._?
(e) 14 NmZ/C ___..,.. _______,_., Question 15 What is the equivalent capacitance of the circuit? (a) 2 pF
(b) 6 ,uF I I ’22,;
(0) 9m? Ml
(d) 12m .
(e) 24;”:  . ‘ 
)1 ,5; F a
5,” F Question 16 A triangular conductor is placed in an originally uniform electric ﬁeld. Which
picture best represents the static eg uipotential lines near the conductor? Question 17 A point charge q is located a distance a from the center of a sphere of radius 2a. A
charge Q is distributed uniformly throughout the volume of the sphere. What is the
magnitude of the electrostatic force between the point charge q and the sphere? (a) F: 47:80 (611—? (b) F = (C) F 216711290 [ti—(22
(d) F 232%] El;
(e) F: 36:38 (it—(3 Question 18 Find the magnitude of the electric ﬁeld at the center of the square in the ﬁgure if
q=8nC and a: 0.1m.
(a) 3.6 . 103N/C.
(b) 5.1 . 103N/C
(c) 7.2  103N/C
(d) 1.4 . 104N/C
(e) 2.2 . 104N/C Question 19 A thin glass rod is bent into a semicircle of radius r. The rod has a uniform charge
per unit length +1 on the upper half and  It on the low half. Find the magnitude of the electric ﬁeld at B. (a) 0 22.
(b) k; A (c) k———
2r 4k 2» (d) ‘3‘: (e) 2k? Question 20 The electric potential varies along the xaxis as shown in the graph. Of the
intervals shown, determine the interval in which Ex has its greatest value. (a) 15 V/m
(b) 12 V/m '
(c) 7V/m E
(d) 6V/m ,l. v
(e) 3 Wm H‘ 7
II ‘ m
an" ’ ﬂ
. E l allllll ' ...
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This note was uploaded on 12/07/2011 for the course PHYS 241 taught by Professor Wei during the Fall '08 term at Purdue.
 Fall '08
 Wei

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