Download PHYS 221 Summer 2011 - Midterm Practice

PHYS 221 Summer 2011 - Midterm Practice Problems
Multiple Choice
Identify the choice that best completes the statement or answers the question.
1. In order for a circuit to respond quickly, its time
5. An RL series circuit has the following components:
constant should be short. In a circuit involving
5.0 mH coil, 1.0  resistor, 12 V battery, ammeter
resistance and capacitance, which of the following
and switch. What is the time constant of this
choices would result in the shortest time constant?
circuit?
a. R = 100 , C = 100 µF
a. 2.5  102 s
b. R = 200 , C = 200 µF
b. 5.0  103 s
c. R = 75 , C = 75 µF
c. 12  103 s
d. R = 300 , C = 50 µF
d. 200 s
2. A “sandwich” is constructed of two flat pieces of
metal (2.00 cm on a side) with a 2.00 mm thick
piece of a dielectric called Rutile ( = 100) in
between them. What is the capacitance? (0 = 8.85
 1012 C2/Nm2)
a. 177 pF
b. 100 µF
c. 8.85 µF
d. 885 nF
6. A series RC circuit has a time constant of 1.0 s. The
battery has a voltage of 50 V and the maximum
current just after closing the switch is 500 mA. The
capacitor is initially uncharged. What is the charge
on the capacitor 2.0 s after the switch is closed?
3. A circuit contains a 6.0 V battery, a 4.0  resistor,
a 0.60 µF capacitor, an ammeter, and a switch all in
series. What will be the current reading
immediately after the switch is closed?
a. 0.99 C
b. 0.48 C
c. 0.43 C
d. 0.86 C
a.
b.
c.
d.
zero
1.5 A
0.75 A
10 A
4. A parallel plate capacitor is attached to a fixed
voltage supply. If the plates are then separated to
double the initial value, what happens to the energy
stored by the capacitor?
a. It doubles since the volume between the plates
doubles.
b. It stays the same since the volume doubles
while the electric field halves.
c. It halves, go figure!
d. It quadruples since both the volume and the
field double in this case.
7. If a 500 W heater carries a current of 4.00 A, what
is the voltage across the ends of the heating
element?
a. 250 V
b. 125 V
c. 0.008 V
d. 2 000 V
8. If C1 = 25 µF, C2 = 20 µF, C3 = 10 µF, and V0 =
21 V, determine the energy stored by C2.
a.
b.
c.
d.
0.72 mJ
0.91 mJ
0.40 mJ
0.32 mJ
9. A proton moving at a speed of 3.8  106 m/s cuts
across the lines of a magnetic field at an angle of
70°. The strength of the field is 0.25  104 T. What
is the magnitude of the force acting on the proton?
(qp = 1.6  1019 C)
a. 1.4  1017 N
b. 9.0  1018 N
c. 5.1  1018 N
d. 2.3  1017 N
10. A 12.0 F capacitor is connected to an AC source
with an rms voltage of 120 V and a frequency of
60.0 Hz. What is the rms current in the capacitor?
a. 0.543 A
b. 0.768 A
c. 1.41 A
d. 0 A
11. The primary winding of an electric train
transformer has 400 turns, and the secondary has
50. If the input voltage is 120 V(rms), what is the
output voltage?
a. 60 V
b. 10 V
c. 15 V
d. 480 V
12. When an electric current exists within a conducting
wire, which of the following statements describes
the condition of any accompanying electric field?
a. must be anti-parallel (opposite direction) to
current flow
b. must be parallel to current flow
c. must be zero
d. must be perpendicular to current flow
13. The number of electric field lines passing through a
unit cross sectional area is indicative of:
a. charge motion.
b. charge density.
c. field direction.
d. field strength.
14. A horizontal wire of length 3.0 m carries a current
of 6.0 A and is oriented so that the current direction
is 50° S of W. The Earth's magnetic field is due
north at this point and has a strength of 0.14  104
T. What is the direction of the force on the wire?
a. out of the Earth’s surface
b. toward the Earth’s surface
c. 40° S of E
d. due east
15. How is the direction of propagation of an
electromagnetic wave oriented relative to the
associated
and
fields?
a. parallel to , perpendicular to
b. parallel to , perpendicular to
c. parallel to both
and
d. perpendicular to both
and
16. A 120 V (rms) source is connected in series with a
20.0  resistor, an 8.8 mH inductor, and a 6.0 F
capacitor. If the source runs at 60 Hz, what is the
impedance of circuit?
a. 445 
b. 439 
c. 20 
d. 400 
17. A radio wave signal, which transmits at a frequency
of 7.20 MHz, has what wavelength? (c = 3.00  108
m/s)
a. 2.4  102 m
b. 41.7 m
c. 28.8 m
d. 4.17 m
18. Suppose two equipotential surfaces are the planes x
= 3 m and x = 5 m. If the potential at the x = 3 m
surface is 10 V and the potential at the x = 5 m
surface is 30 V, what is the magnitude of the
electric field between the two surfaces?
a. 10 N/C
b. 15 N/C
c. 40 N/C
d. 20 N/C
19. A proton initially moves left to right long the x axis
at a speed of 2.00  103 m/s. It moves into an
electric field, which points in the negative x
direction, and travels a distance of 0.200 m before
coming to rest. What acceleration magnitude does
the proton experience?
a. 2.67  1011m/s2
b. 6.67  103 m/s2
c. 9.33  109 m/s2
d. 1.00  107 m/s2
20. Two point charges of values +3.4 C and +6.6 C
are separated by 0.10 m. What is the electrical
potential at the point midway between the two
charges? (ke = 8.99  109 Nm2/C2)
a. +0.90  106 V
b. 0.90  106 V
c. +1.8  106 V
d. +3.6  106 V
21. The constant ke, which appears in Coulomb’s law
formula, is equivalent dimensionally to which of
the following?
a. Nm/C
b. N/C
c. Nm2/C2
d. N/C2
22. One time constant after an RL circuit has its switch
closed, how does the current I in it compare to the
maximum current Imax that occurs for this circuit?
a. I < Imax/2
b. I > Imax/2
c. Without knowing R and L, this cannot be
determined.
d. I = Imax/2
23. According to Lenz’s law the direction of an
induced current in a conductor will be that which
tends to produce which of the following effects?
a. produce a greater heating effect
b. produce the greatest voltage
c. oppose the effect which produces it
d. enhance the effect which produces it
24. Which of the following combinations of circuit
components can be used to make a tuner for a radio,
to select the desired frequency?
a. fixed inductor, variable resistor
b. fixed resistor, variable inductor
c. fixed capacitor, variable resistor
d. fixed inductor, variable capacitor
25. A 10.0 F capacitor is attached to a 20 V power
supply. How much energy is stored in the
capacitor?
a. 2.0  104 J
b. 5.2  104 J
c. 2.0  103 J
d. 1.2  103 J
26. The first bar magnet is attached solidly to the
surface and its length is aligned with the x axis. To
the right of the first magnet a short distance away is
a second bar magnet with its center placed on the x
axis and its length perpendicular to the x axis. The
second magnet is free to move. Once placed in
position at rest, which best describes the motion of
the second magnet?
a. The magnet will move toward the fixed
magnet.
b. The magnet will move away from the fixed
magnet.
c. The magnet will not move.
d. The magnet will start to rotate.
27. A beam of polarized light of intensity I0 passes
through a sheet of ideal polarizing material. The
polarization axis of the beam and the transmission
axis of the sheet differ by 30°. What is the
intensity of the emerging light?
a. 0.50 I0
b. 0.25 I0
c. 0.75 I0
d. 0.87 I0
28. The dielectric strength of Rutile is 6.0  106 V/m,
which corresponds to the maximum electric field
that the dielectric can sustain before breakdown.
What is the maximum charge that a 1010 F
capacitor with a 1.0 mm thickness of Rutile can
hold?
a. 6.0 C
b. 0.60 µC
c. 0.30 mC
d. 1.7 nC
29. A circular loop carrying a current of 1.0 A is
oriented in a magnetic field of 0.35 T. The loop has
an area of 0.24 m2 and is mounted on an axis,
perpendicular to the magnetic field, which allows
the loop to rotate. What is the torque on the loop
when its plane is oriented at a 25° angle to the
field?
a. 0.010 Nm
b. 0.051 Nm
c. 4.6 Nm
d. 0.076 Nm
30. The current in a coil with a self-inductance of 1.5
mH increases from 0 to 1.0 A in a tenth of a
second. What is the induced emf in the coil?
a. 15 mV
b. 0.30 V
c. 0.10 V
d. 30 mV
31. A solid conducting sphere of 10 cm radius has a net
charge of 20 nC. If the potential at infinity is taken
as zero, what is the potential at the center of the
sphere?
a. 360 V
b. 1.8  103 V
c. 36 V
d. >1.8  104 V
32. Electrons in an x-ray machine are accelerated from
rest through a potential difference of 50,000 V.
What is the kinetic energy of each of these
electrons in eV?
a. 50 keV
b. 330 eV
c. 80 eV
d. 50 eV
33. A high voltage transmission line of diameter 2 cm
and length 200 km carries a steady current of 1000
A. If the conductor is copper with a free charge
density of 8  1028 electrons/m3, how long does it
take one electron to travel the full length of the
cable? (e = 1.6  1019 C)
a. 8  102 s
b. 8  108 s
c. 8  104 s
d. 8  106 s
34. The units T·m2/s are equivalent to:
a. webers.
b. W.
c. N/m.
d. V.
35. A superconducting wire carries a current of 104 A.
Find the magnetic field at a distance of 1.0 m from
the wire. (µ0 = 4  107 Tm/A)
a. 1.6  102 T
b. 2  103 T
c. 8  103 T
d. 3.2  102 T
36. Two point charges are separated by 10.0 cm and
have charges of +2.00 µC and 2.00 µC,
respectively. What is the electric field at a point
midway between the two charges? (ke = 8.99  109
N·m2/C2)
a. 7.19  106 N/C
b. zero
c. 28.8  106 N/C
d. 14.4  106 N/C
37. A radar pulse returns 3.0  104 seconds after it is
sent out, having been reflected by an object. What
is the distance between the radar antenna and the
object? (c = 3.00  108 m/s)
a. 6.0  104 m
b. 1.0  104 m
c. 9.0  104 m
d. 4.5  104 m
38. Three resistors, each of different value, are used in
a circuit with a power source supplying 12 volts.
For which of the following resistor combinations is
the total power supplied the greatest?
a. two of the resistors in parallel with the third
resistor in series with the parallel pair
b. all three resistors in series
c. This cannot be found until it is known which
resistor is in series with the parallel pair.
d. all three resistors in parallel
39. Three resistors connected in series have individual
voltages labeled V1, V2 and V3, respectively.
Which of the following expresses the value of the
total voltage VT taken over the three resistors
together?
a. VT = (1/V1 + 1/V2 + 1/V3)1
b. VT = (1/V1 + 1/V2 + 1/V3)
c. VT = V1 = V2 = V3
d. VT = V1 + V2 + V3
40. Which of the following best characterizes electrical
insulators?
a. electric charges move freely
b. charges on the surface don’t move
c. high tensile strength
d. good heat conductors
41. The direction of the force on a current carrying wire
located in an external magnetic field is which of the
following?
a. perpendicular to the field
b. perpendicular to the current
c. Both choices A and B are valid.
d. None of the above are valid.
46. An initially uncharged hollow metallic sphere with
radius of 5 cm has a small object with a charge of
+10 µC carefully placed at the center of the sphere
through a hole in the latter’s surface. What charge
resides inner surface of the sphere?
a. 10 µC
b. +10 µC
c. 4000 µC
d. zero
47. Four charges are at the corners of a square, with B
and C on opposite corners. Charges A and D, on the
other two corners, have equal charge, while both B
and C have a charge of +1.0 C. What is the charge
on A so that the force on B is zero?
42. If three 4.0 µF capacitors are connected in parallel,
what is the combined capacitance?
a. 0.46 F
b. 8.0 F
c. 12 F
d. 0.75 F
43. The current in an electron beam in a cathode-ray
tube is measured to be 70 µA. How many electrons
hit the screen in 5.0 s? (e = 1.6  1019 C)
a. 2.2  1011 electrons
b. 2.2  1015 electrons
c. 8.8  1013 electrons
d. 8.8  1018 electrons
44. If C = 36 µF, determine the equivalent capacitance
for the combination shown.
a.
b.
c.
d.
36 µF
24 µF
32 µF
28 µF
45. Q1 has 50 electric field lines radiating outward and
Q2 has 100 field lines converging inward. What is
the ratio Q1/Q2?
a. 2
b. 2
c. 1/2
d. 1/2
a.
b.
c.
d.
0.71 C
0.35 C
0.50 C
1.0 C
48. Two parallel wires carry the a current I in the same
direction. Midway between these wires is a third
wire, also parallel to the other two, which carries a
current 0.5 I, but in the direction opposite from the
first two wires. In which direction are the net forces
on the outer wires?
a. Both forces are away from the center wire.
b. Both forces on the two wires are in the same
direction in space.
c. Both forces are toward the center wire.
d. Since the net forces are zero, there is no
direction.
49. Three equal positive charges are placed on the
x-axis, one at the origin, one at x = 2 m, and the
third at x = 4 m. Of the following points, which has
the greatest magnitude electric field?
a. x = 5 m
b. x = 1 m
c. x = 3 m
d. The electric field has the same magnitude at all
three positions.
50. The unit of electrical potential, the volt, is
dimensionally equivalent to:
a.
b.
c.
d.
JC.
J/C.
FC.
C/J.
51. A transformer is to be designed to increase the 30
kV (rms) output of a generator to the transmission
line voltage of 345 kV (rms). If the primary
winding has 80 turns, how many turns must the
secondary have?
a. 920
b. 70
c. 6
d. 9200
52. A straight wire of length is oriented east-west
and is in a magnetic field B pointing north. The
wire is moving downward at a constant speed v.
Which end of the rod is positively charged?
a. neither
b. the east end
c. both ends
d. the west end
53. A copper wire of length 25 cm is in a magnetic
field of 0.20 T. If it has a mass of 10 g, what
minimum current through the wire would cause a
magnetic force equal to its weight?
a. 2.0 A
b. 1.3 A
c. 4.9 A
d. 1.5 A
54. An electron moves through a region of crossed
electric and magnetic fields. The electric field E =
2000 V/m and is directed straight down. The
magnetic field B = 0.80 T and is directed to the left.
For what velocity v of the electron into the paper
will the electric force exactly cancel the magnetic
force?
a.
b.
c.
d.
2500 m/s
8000 m/s
4000 m/s
5000 m/s
55. An AC voltage source, with a peak output of 200
V, is connected to a 50  resistor. What is the rate
of energy dissipated due to heat in the resistor?
a. 200 W
b. 400 W
c. 566 W
d. 800 W
56. A proton (+1.6  1019 C) moves 10 cm on a path in
the direction of a uniform electric field of strength
3.0 N/C. How much work is done on the proton by
the electrical field?
a. 4.8  1020 J
b. zero
c. 4.8  1020 J
d. 1.6  1020 J
57. A loop of area 0.250 m2 is in a uniform 0.0200 T
magnetic field. If the flux through the loop is 3.83 
10-3 T·m2, what angle does the normal to the plane
of the loop make with the direction of the magnetic
field?
a. 37.5°
b. This is not possible.
c. 40.0°
d. 50.0°
58. How can a charged object attract an uncharged
object made of non-conducting material?
a. The uncharged object must somehow gain an
unlike charge.
b. The uncharged object must somehow gain a
like charge.
c. Attraction of an insulator is not possible.
d. The charges in the uncharged object can
become polarized.
59. A thin uncharged conducting spherical shell has a
charge q carefully placed at its center through a
small hole in the shell. The charge q does not
touch the shell. What is the charge on the shell?
a. q
b. 0
c. 2q
d. q
60. If the distance between two point charges is tripled,
the mutual force between them will be changed by
what factor?
a. 3.0
b. 9.0
c. 1/9
d. 0.33
61. A proton is released such that its initial velocity is
from right to left across this page. The proton’s
path, however, is deflected in a direction toward the
bottom edge of the page due to the presence of a
uniform magnetic field. What is the direction of this
field?
a. into the page
b. out of the page
c. from bottom edge to top edge of the page
d. from right to left across the page
62. An AC series circuit contains a resistor of 20 , a
capacitor of 0.75 F and an inductor of 120 mH.
What frequency should be used to create a
resonance condition in the circuit?
a. 320 Hz
b. 530 Hz
c. 640 Hz
d. 160 Hz
63. A 10 turn square coil of area 0.036 m2 and a 20 turn
circular coil are both placed perpendicular to the
same changing magnetic field. The voltage
induced in each of the coils is the same. What is
the area of the circular coil?
a. 0.018 m2
b. 0.60 m2
c. 0.036 m2
d. 0.072 m2
64. A current in a long, straight wire produces a
magnetic field. The magnetic field lines:
a. go out from the wire to infinity.
b. form circles that go around the wire.
c. come in from infinity to the wire.
d. form circles that pass through the wire.
65. The Earth is 1.49  1011 m from the Sun. If the solar
radiation at the top of the Earth's atmosphere is
1340 W/m2, what is the total power output of the
Sun?
a. 2.34  1030 W
b. 3.74  1026 W
c. 7.48  1027 W
d. 6.62  1026 W
66. Three loops of wire, one circular, one rectangular,
and one square, are made from identical lengths of
wire. If the loops are in the same increasing
magnetic field perpendicular to the plane of the
coils, which loop has the greatest induced emf?
a. the square one
b. All three would have the same emf induced.
c. the circular one
d. the rectangular one
67. In the typical household AC voltage of 120 V, what
is the peak voltage?
a. 120 V
b. 85 V
c. 240 V
d. 170 V
68. If a 9.0 V battery, with negligible internal
resistance, and an 18  resistor are connected in
series, what is the amount of electrical energy
transformed to heat per coulomb of charge that
flows through the circuit?
a. 72 J
b. 0.50 J
c. 9.0 J
d. 3.0 J
69. An electron and a proton are each released from
rest in the same uniform electric field. The electron
moves a distance delectron and the proton moves a
distance dproton as each particle’s kinetic energy
increases by 1.6 eV. How do delectron and dproton
compare?
a. delectron = dproton
b. delectron < dproton
c. delectron > dproton
d. The answer depends on the direction of the
electric field.
70. An electron in a cathode ray tube is accelerated
through a potential difference of 5.0 kV. What
kinetic energy does the electron gain in the
process? (e = 1.6  1019 C)
a. 8.0  1022 J
b. 1.6  1016 J
c. 1.6  1022 J
d. 8.0  1016 J
71. A 50  resistor, a 0.1 H inductor, and a 10 µF
capacitor are connected in series to a 60 Hz source.
The rms current in the circuit is 3 A. Find the rms
voltage across the resistor, the inductor, and the
capacitor.
a. 150 V, 113 V, 562 V (all rms)
b. 0.06 V, 80 V, 562 V (all rms)
c. 150 V, 113 V, 796 V (all rms)
d. 60 V, 80 V, 796 V (all rms)
77. Two protons, each of charge 1.60  1019 C, are
2.00  105 m apart. What is the change in potential
energy if they are brought 1.00  105 m closer
together? (ke = 8.99  109 N·m2/C2)
a. 3.20  1019 J
b. 1.60  1014 J
c. 1.15  1023 J
d. 3.20  1016 J
72. A bar magnet is falling through a loop of wire with
constant velocity. The north pole enters first. As the
south pole leaves the loop of wire, the induced
current (as viewed from above) will be:
a. along the length of the magnet.
b. counterclockwise.
c. clockwise.
d. zero.
78. A proton moving with a speed of 3.0  105 m/s
perpendicular to a uniform magnetic field of 0.20 T
will follow which of the paths described below? (qp
= 1.6  1019 C and mp = 1.67  1027 kg)
a. a circular path of 1.6 cm radius
b. a circular path of 3.1 cm radius
c. a straight line path
d. a circular path of 6.3 cm radius
73. What is the stored energy in a 0.50 mH coil
carrying a current of 4.0 A?
a. 2.0  103 J
b. 12  103 J
c. 8.0  103 J
d. 4.0  103 J
79. The force on a charged particle created by its
motion in a magnetic field is maximum at what
angle between the particle velocity and field?
a. 45°
b. zero
c. 180°
d. 90°
74. In an AC series circuit, the current in a pure resistor
differs in phase with the applied voltage by what
angle?
a. 180°
b. 45°
c. 90°
d. zero
80. If R1 < R2 < R3, and if these resistors are connected
in series in a circuit, which one dissipates the
greatest power?
a. R2
b. All are equal in power dissipation.
c. R1
d. R3
75. The unit of electric current, the ampere, is
equivalent to which of the following?
a. m
b. V
c. V/s
d. V/
81. A 0.25 F capacitor is connected to a 400 V
battery. Find the charge on the capacitor.
a. 0.040 C
b. 1.0  104 C
c. 0.020 C
d. 1.2  1012 C
76. An electromagnetic wave with a peak magnetic
field component of 1.5  107 T carries what
average power per unit area? (0 = 4  107
Tm/A, 0 = 8.85  1012 C2/Nm2 and c = 3.00 
108 m/s)
a. 1.3 W/m2
b. 12 W/m2
c. 2.7 W/m2
d. 3.0 W/m2
82. Peak values for a neodymium-glass laser are 600 J
for 1 nanosecond . If the cross-section of the laser
beam is 1 cm2, what are the maximum values of E
and B? (µ0 = 4  107 Tm/A, c = 3.00  108 m/s)
a. 2  109 V/m, 2 T
b. 4  108 V/m, 2 T
c. 2  109 V/m, 7 T
d. 4  108 V/m, 7 T
83. A superconducting solenoid is to be designed to
generate a magnetic field of 5.00 T. If the solenoid
winding has 1000 turns/m, what is the required
current? (µ0 = 4  107 Tm/A)
a. 1990 A
b. 3980 A
c. 1000 A
d. 5000 A
88. An uncharged conductor is supported by an
insulating stand. I pass a positively charged rod
near the left end of the conductor, but do not touch
it. The right end of the conductor will be:
a. attracted.
b. neutral.
c. negative.
d. positive.
84. The average distance of the electron from the
proton in the hydrogen atom is 0.51  1010 m.
What is the electric field from the proton’s charge
at the location of the electron? (ke = 8.99  109
Nm2/C2, e = 1.6  1019 C)
a. 1.0  106 N/C
b. 8.8  108 N/C
c. 3.2  102 N/C
d. 5.5  1011 N/C
89. How is the energy stored in a current-carrying
inductor related to the current value, I?
a. directly proportional to I
b. directly proportional to I 1/2
c. inversely proportional to I
d. directly proportional to I 2
85. Two capacitors with capacitances of 1.0 C and
0.50 F, respectively, are connected in series. The
system is connected to a 100 V battery. What
charge accumulates on the 1.0 F capacitor?
a. 33 C
b. 150 C
c. 100 C
d. 50 C
86. Two wires with the same resistance have the same
diameter but different lengths. If wire 1 has length
L1 and wire 2 has length L2, how do L1 and L2
compare if wire 1 is made from copper and wire 2
is made from aluminum? The resistivity of copper
is 1.7  10-5 ·m and the resistivity of aluminum is
2.82 10-5 ·m.
a. L1 = 1.7 L2
b. L1 = 0.36 L2
c. L1 = 0.60 L2
d. L1 = 2.8 L2
87. A current in a solenoid coil creates a magnetic field
inside that coil. The field strength is directly
proportional to:
a. the current.
b. Both A and B are valid choices.
c. the coil area.
d. None of the above choices are valid.
90. Of the various types of electromagnetic radiation,
the shortest wavelengths are the most penetrating
through all forms of matter. Which of the following
is it?
a. gamma
b. ultraviolet
c. visible light
d. infrared
91. A proton with initial kinetic energy E is moving in
circular motion in a uniform magnetic field. When
it has completed one eighth of a revolution, what is
its kinetic energy?
a. 1.4 E
b. 0.71 E
c. The value is not given.
d. E
92. Wire A and Wire B are each carrying the same
current. If the diameter of Wire A is twice that of
Wire B, how does the drift velocity vdA in Wire A
compare to that in in Wire B?
a. vdA = vdB /4
b. vdA = vdB /2
c. vdA = 2 vdB
d. vdA = vdB
93. In an AC series circuit the capacitive reactance is
200  and frequency is 100 Hz. What is the
capacitance?
a. 8.0 F
b. 6.28 F
c. 50.0 F
d. 3.2 F
94. An AM radio tuning circuit has a coil with an
inductance of 6.00 mH and a capacitor set at 7.50 
106 F. What frequency will it detect?
a. 550 kHz
b. 1060 kHz
c. 1520 kHz
d. 750 kHz
95. Unpolarized light is passed through polarizer 1.
The light then goes though polarizer 2 with its
plane of polarization at 45.0° to that of polarizer 1.
Polarizer 3 is placed after polarizer 2. Polarizer 3
has its plane of polarization at 45° to the plane of
polarization of polarizer 2 and at 90° to that of
polarizer 1. What fraction of the intensity of the
original light gets though the last polarizer?
a. 0.707
b. 0.250
c. 0.125
d. 0.500
96. A 6.0 C charge is placed at the origin and a
second charge is placed on the x axis at x = 0.30 m.
If the resulting force on the second charge is 5.4 N
in the positive x direction, what is the value of its
charge?
a. –9.0 C
b. –9.0 nC
c. 9.0 nC
d. 9.0 C
97. In the inductor of a 60 Hz AC series circuit, the
peak voltage precedes the peak current in each
cycle by what time interval?
a. 1.7  103 s
b. 4.2  103 s
c. 2.1  103 s
d. 8.3  103 s
PHYS 221 Summer 2011 - Midterm Practice Problems
Answer Section
MULTIPLE CHOICE
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C
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B
C
B
C
B
B
A
A
C
B
D
B
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B
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D
C
C
B
C
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C
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C
B
D
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B
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B
C
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C
B
B
C
A
B
D
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B
A
B
A
A
B
A
C
D
B
C
A
B
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B
B
C
D
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D
D
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C
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97.
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D
A
D
A
A
D
C
D
B
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1
1
1
1
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1
1
2
2
2
2
2
2
2