This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: Physics 241
Fall 2009
Exam 1 September 30, 2009 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. . Sign Name Student ID If during the exam you feel there is an equation that should be on the equation sheet contact one of
the exam proctors. Your request will be considered and placed before all the students, if your
request is deemed acceptable. If you feel any of the questions are ambiguous or unclear, complete the problems according to your
interpretation of the problem. Include all your work and calculations clearly. Turn in the paper
version of the exam along with your optical scan sheet. This will allow you to argue your case, if
your solution does not agree with that given as the answer. Physics 241, Exam 1 Equation Sheet
2 2
k=9109N”: k= 1 30:91012 C 2 1eV=1.610"9J e=1.610“°C
C 471780 Nm
~ 614 a a q A ~ * * d4 A 0 "
F=k 11.2% E=kr—2‘r E(p)=ZE,.p dE=kr—2‘r 13:2; 113:;
d a Q b” _ .. a a 
¢=fE~ﬁdA gSEiidA=— AV=V,,—1{,=—fEdz dU=—F~dl F=qE
S S 80 a
dvzd—U_—E.df VJ?? {1:251 Ex=—d—V =_£n_/_ Ez=—d—V
go r r,. dx " dy dz
2
EPA: V= E12 (1:9 C=8"A V=Qd U=lg=lQV=lCV2
Ar r V d 80A 2 C 2 2
l 2 " "
u=EsaE 8=K£0 E=—VV
. . dr 1 dr
j cos(9) d9 = sm(6) jszn(9)d9 = — cos(6) —2~ = — — — = 1n(r) jrde = r6
r I" l“ ‘ 2
r Jdr=r Irdr=2— Question 1. A 20 pC (20x10"2C) point charge q is placed next to another charge Q of 1 C at a distance d as
shown. What is the ratio Fq/FQ of the magnitude of the electric force acting on q to that of the
electric force acting on Q? a) 20x10"2C b) 4.5x10“6C c) 1 d) 2.2x105C e) SXIO'OC Question 2. _
In the region of space where there is a non—uniform electric field E as shown, how will the dipole
move? a) The dipole moves oscillates back and forth with
respect to E. b) Dipole moves towards smaller E c) Dipole moves toward larger E . / E d) Dipole moment aligns with E and moves towards
large B e) Dipole moment aligns with E and moves towards
smaller E Question 3.
In the Figure all the capacitors are identical. Which combination has the largest equivalent
capacitance? Hr 311+ +le
”1% all? ‘ Question 4
The upper half of a ring is uniformly charged with a positive charge density +0, while the lower half is uniformly charged with a charge density of —0'. What is the direction of the electric field at
the point X on the perpendicular axis of the ring as shown? a) E is Zero
b) To the Right
c) To the Left d) Up ..._..__.>< _______ e) Down Question 5.
The graph on the right shows the electric
potential, V(x) as a function of distance x. Which of the graphs represents the electric
field, E(x)? (13) E00
(‘1) E00 Question 6. 56
01
+26
d
o Three very large non—conducting charged planes are parallel to each other with the shown charge densities. If the plane at the bottom has an electric potential of zero, what is the electric potential of
the plane in the middle? d
(a) +0'— (b) —30'~£1— (c) —40'1
80 80 80
(d) —0'1 (e) +2041
80 80
Question 7 Two conducting spheres are placed far apart
but are connected by a thin and negligible
conducting wire. A charge Q is place on the
spheres. What is the ratio EJER of the electric
fields on the surface of the spheres? . z ” thinwire
(hlntQ=QR+Qr)
E R—~r E R—r E r
a) _!_= Q2 I?) _"= C) _;=___
ER R+r R R+r ER R
E R E R
d) —’=— e) ~L=—Q
ER r a r Question 8.
Two charged, parallel ﬁat conducting plates are spaced 1 cm apart. The potential difference
between the plates is 500 volts. An electron is projected from one surface directly towards the
other. What is the initial speed of the electron if it stops just at the surface of the second?
(Meltcum: 9XI031kg) a) 1.8x1014m/sec b) 1.37:107 m/sec c) 3.0x10’3 m/sec d) 500 m/sec e) 4.5x103 m/sec Question 9. An uncharged penny is brought into an external electric ﬁeld of magnitude 2,200 V/rn directed
perpendicular to its faces. Find the magnitude of the charge density induced on each face of the
penny, assuming the faces are planes. a) 72 nC/m2 b) 47 pC/m2 c) 48 nC/m2 d) 20 nC/m2 e) 20 pC/m2 Question 10. A hollow conducting spherical shell with a ﬁnite thickness has a charge placed at its center. If the
potential is deﬁned to be zero at inﬁnity what is the potential at a point P within the conductor at a
radius r from the center of the shell? (I) k1 b) k?— c) k3
r a b
d) kg %+%) 6) zero Question 11.
Evaluate the integral @8025} o dﬁ
over the surface in the ﬁgure.
a) +9q ’
b) +3q
0) —3q
60 —9q e) +6q Question 12. Two positive 2.0mC charges are placed as shown in part(a). The [“7 4 f5) .
distance from each charge to the . (a M .0? .a 4/ m
point P is 0.04m. Then the charges P e a ”t
are rearranged as shown in part (b). 40/“: 29:46 E 2.9;;
which statement is nowtrue after '
the rearrangement concerning E and
V at the point P? quC. .0991. a) The electric ﬁeld and the electric potential are both zero. b) E=0, but V is the same as before the charges were moved. c) V=0, but E is the same as before the charges were moved. (I) E is the same as before the charges were moved, but V is less than before. e) Both E and V have changed and neither is zero. , Question 13.  A parallel plate capacitor with a separation distance between the plates of d is initially connected to
a battery and completely charged having an energy density mg. The battery remains connected and
the distance between the plates is increased to 3d. What is the new value of the energy density (joules/m3). a)9uE (9)3953 cm d)? a)? For Questions 14, and 15. Consider the concentric metal sphere and spherical shells that are shown in the ﬁgure. The inner most solid
sphere that has radius R1. A spherical shell surrounds the sphere and has an inner radius R2 and an outer
radius R3. The sphere and shell are both surrounded by a second spherical shell that has an inner radius R4
and an outer Radius R5. None of these objects is initially charged. Then, a negative charge, —Q is placed on the inner most sphere (a)
and a positive charge +Q is placed on the outer most shell(c). Question 14.
From the table which row gives the correct ﬁnal charge distribution once the charges come to
equilibrium on each surface of the sphere and shells. SurfacesI Mﬁﬂﬂﬁ um
nun":
unnu Question 15. Which regions have no electric field?
a) Only Regions 1, 3 and 5
h) Only Regions 1, 3, 4, and 5
c) Only Regions 1,2, 3, and 5
(1) Only Regions 1, 3, 5, and 6 6) Only Regions 1,3, 4, 5 and 6 Question 16.
A uniformly charged sphere has a potential on its surface of 1000 volts. At a radial distance of 3
meters from this surface, the potential is 200 volts. What is the radius of the sphere? a) 0.1 m b) 0.25 m c) 0.5 m d) 0.75 m e)1.0m Question 17.
During the process described by the photoelectric effect, ultraviolet light can be used to charge a
piece of metal. If this light is incident on a slab of conducting material and the electrons are ejected
with enough energy that they escape the surface of the metal, how long before the metal has a net
charge of 1.5nC if 1.0){108 electrons are ejected per second? a) 5400 seconds b) 1500 seconds c) 640 seconds (1) 94 seconds e) 7 seconds Question 18. A ring of radius R has a charge distribution
1(9) = +JLOSin(9) what is the electric ﬁeld E at the center of the ring?
(Note: Integral table on equation sheet) r 1 2 R » 1 2 R a 1 2
E:— —"s' — " b E=— —01 —" E=+ —° ‘
a) 8 0 R ”Kn” ) 880 R “(an 6) 41150 R 3’
_ 1 1 2 A —. 1 2 .
d E=— + —° E=— —0
) (830 4 3R)” 8) 880R y ~ Question 19.
A ﬂat sheet of paper of area 1.5m2 is oriented so that the plane of the sheet is at an angle of B=25 degrees with respect to a uniform electric field of magnitude 35 N/C. What is the magnitude of the electric flux throu h the sheet?
a) 3.0 Nm IC b)1.8 NmZIC
c) 22.2 NmZIC d) 35 NmZIC e) 140 NmZIC Question 20. A square parallel plate capacitor with plate
separation d is ﬁlled with a long thin dielectric
strips so that each strip has an increasing
dielectric constant as a function of x such that at
x=0 k=1, K'(X) = (KOX +1) What is the capacitance of this capacitor?
(Hint: assume each strip has a thickness dx
and the area of each strip is L dx) 2 2 a)c=._£2§_i‘o_ b)C=8"L (K"L+1)
ln(Kad+1) d 2 d)C = d (””1“ +1) e) C = some exP(‘("od + 1)) 8L2 2 D c)C= 2
80L K", ...
View
Full Document
 Spring '10
 Yu
 Physics

Click to edit the document details